V. Translate the sentences into English

2. Две прямые называются перпендикулярными, если они пересе­каются под прямым углом.

3. Какой угол называется прилежащим?

4. Докажите, что вертикальные углы равны.

5. Сумма трех этих углов равна 270°.
VI. Read the sentences and think of a word which best fits each space.
1. An angle is a ... of two lines (the sides or …) meeting at a point called the vertex.

2. Flat (or ...) angle means half a ... turn.

3. An obtuse angle is greater than an ... angle.

4. The measure of a ... angle is between 180°and 360°.

5. Angles are classified according to their....

6. Clockwise means the ... in which the hands of a clock rotate.

7. The largest angle is the ... angle being 360 degrees.

7. 
   Answer the questions on the text "Angles".
   

1. 
   What is an angle?
   
2. 
   Can one say that an angle is regarded as the measure of rotation in­volved in moving from one initial axis to coincide with another final axis?
   
3. 
   What are characteristics of a null angle?
   
4. 
   An acute angle is an angle between 0° and 90°, isn't it?
   
5. 
   What are characteristics of an obtuse angle?
   
6. 
   What are characteristics of a reflex angle?
   
7. 
   Is there any difference between the angle of depression and the angle
   of elevation?
   

The distance from the center of a regular polygon to one of its vertices is called the long radius, which is also a radius of the circumcircle of the poly­gon. The perpendicular distance from the center to one of the sides is called the short radius or apothem, which is also the radius of the inscribed circle of the polygon.

A regular star polygon is a figure formed by joining every m-th point, starting with a given point, of the n points that divide a circle's circumference into n equal parts, where m and n are relatively prime, and n is equal two or greater than 3. This star polygon is denoted by {m/n}. When m = 1, the result­ing figure is a regular polygon. The star polygon {5/2} is the pentagram.

1. 
   Read and decide which of the statements are true and which are false.
   

2. No sides of a polygon usually intersect.

3. All the interior angles of a convex polygon are greater than or equal to180.

4. An equilateral polygon is a polygon whose no sides are equal.

5. An equiangular polygon is a polygon whose all interior angles are equal.

6. The regular polygon is both equilateral and equiangular.

7. The perpendicular distance from the center to one of the sides is called the long radius.

8. The long radius is also the radius of the inscribed circle of the poly­gon.

9. The star polygon is usually denoted by {m/n}.

2. 
   Match the terms from the left column and definitions from the right column:
   

3. 
   Give the Russian equivalents of the following words and word
   

1. 
   exterior angle
   
2. 
   circumcircle
   
3. 
   perpendicular
   
4. 
   apothem
   
5. 
   inscribed circle
   
6. 
   star polygon
   
7. 
   relatively prime
   
8. 
   regular star polygon
   
9. 
   pentagram
   
10. 
    closed plane figure
    
11. 
    interior angle
    
12. 
    convex polygon
    
13. 
    concave polygon
    
14. 
    equilateral polygon
    
15. 
    equiangular polygon
    
16. 
    equilateral triangle
    
17. 
    regular polygon
    
18. 
    long radius
    

4. 
   Give the English equivalents of the following words and word combinations:
   

равносторонний треугольник, правильный треугольник, замкнутая плоская фигура, апофема (радиус вписанного круга), вписанная окруж­ность, внутренний угол, взаимно простые, радиус описанного круга, вы­пуклый многоугольник, описанная окружность, пентаграмма (пятиугольная звезда), равноугольный многоугольник, вогнутый многоугольник, много­угольник в виде звезды, правильный многоугольник в виде звезды, внеш­ний угол, перпендикуляр, равносторонний многоугольник.

4. 
   Answer the questions on the text.
   

1. What figure is usually understood in geometry as a polygon?

2. No two sides in a polygon intersect, do they?

3. What is the usual measure of the interior angles of a convex polygon and of a concave polygon respectively?

4. A polygon that has all its sides equal is an equiangular polygon, isn't it?

5. A polygon in which all its interior angles are equal is an equilateral polygon, isn't it?

6. Must an equilateral polygon be equiangular?

4. 
   Read and translate the sentences and the questions.
   

1. This figure is formed by three points.

2. This term is usually used to denote a closed plane figure.

3. This polygon has only one interior angle.

4. This polygon is said to be regular.

5. The points divide a circle's circumference into equal parts.

6. What are the main characteristics of a regular polygon?

7. The distance from the center of a regular polygon to one of its vertices is called the long radius, isn't it?

8. Is the apothem also the radius of the inscribed circle of the polygon?

9. What figure is called a regular star polygon?

10. What figure is usually understood in geometry as a polygon?

4. 
   Match the words and the definitions:
   

interior angle, convex polygon, exterior angle, circumcircle, pentagram, concave polygon, inscribed circle, regular polygon, long radius.

1) An angle formed outside a polygon.

2) A circle circumscribed about a given polygon.

3) A polygon that has all its angles less than or equal to 180°.

4) An angle between two sides of a polygon lying within the polygon.

5) A symmetrical five-pointed star polygon.

6) A polygon that has at least one interior angle greater than 180°.

7. 
   Translate the text into English.
   

Правильный выпуклый многоугольник является одновременно вписанным в окружность и описанным около нее.

Углом выпуклого многоугольника при определенной вершине называется угол, образованный его сторонами, которые сходятся в этой вершине. Внешним углом выпуклого многоугольника при данной вершине называется угол, смежный с внутренним углом многоугольника при этой вершине.

TEXT IV.
THE CARTESIAN COORDINATE SYSTEM
The Cartesian coordinate system is a coordinate system in which the position of a point is determined by its distances from reference lines (axes). In two dimensions two lines are used; commonly the lines are at right angles, forming a rectangular coordinate system. The horizontal axis is x-axis and the vertical axis is the y-axis. The point of intersection O is the origin of the coor­dinate system. Distances along the x-axis to the right of the origin are usually taken as positive, distances to the left - as negative. Distances along the y-axis above the origin are positive; distances below are negative. The position of a point anywhere in the plane can then be specified by two numbers, the coordi­nates of the point, written (x,y). The x-coordinate (or abscissa) is the distance of the point from the y-axis in a direction parallel to the x-axis (i.e. horizon­tally). The y-coordinate (or ordinate) is the distance of the point from the x-axis in a direction parallel to the y-axis (vertically). The origin O is the point (0,0). The two axes divide the plane into four quadrants, numbered anticlock­wise starting from the top right (positive) quadrant.

Cartesian coordinates were first introduced in the 17th century by Rene Descartes. Their discovery allowed the application of algebraic methods to geometry and the study of hitherto unknown curves. As a point in Cartesian coordinates is represented by an order pair of numbers, so is a line represented by an equation. Thus, y = x represent a set of points for which the x-coordinate equals the y-coordinate; i.e. y = x is a straight line through the origin at 45° to the axes. Equations of higher degree represent curves; for example, x² + y² = 4 is a circle of radius 2 with its center at the origin. A curve drawn in a Cartesian coordinate system for a particular equation or function is a graph of the equa­tion or function.

The axes in planar Cartesian coordinate system need not necessarily be at right angles to each other. If the x- and y- axes make an angle than 90° the system is said to be an oblique coordinate system. Distances from the axes are then measured along lines parallel to the axes.

Cartesian coordinate system can also be for three dimensions by in­cluding a third axis - z-axis - through the origin perpendicular to the other two. The position of point is then given by three coordinates (x,y,z). The coordinate axes may be left-handed or right-handed, depending on the way positive directions are given to the axes. In a right-handed system if the thumb of the right hand points in the positive direction of the x-axis, the first and second fingers can be pointed in the positive direction of the y- and z-axes respectively. A left-handed system is the mirror image of this (i.e. determined by using the left hand).

1. 
   Read and decide which of the statements are true and which are false.
   

2. 
   The vertical axis on the coordinate system is x-axis and the horizontal
   axis is the y-axis.
   
3. 
   The point of intersection О is the origin of the coordinate system.
   
4. 
   Distances along the x-axis to the right of the origin are usually taken
   as negative and distances to the left - as positive.
   
5. 
   The position of a point anywhere in the plane is specified by at least
   four numbers.
   
6. 
   The abscissa is the distance of the point from the y-axis in the vertical
   direction.
   

7. 
   The ordinate is the distance of the point from the x-axis in the hori­zontal direction.
   
8. 
   The two axes divide the plane into four quadrants numbered clock­wise starting from the top left (negative) quadrant.
   
9. 
   If a point in Cartesian coordinates is represented by an order pair of
   numbers, but a line is represented by an equation.
   

10. 
    The axes in planar Cartesian coordinate system can be at various right angles to each other (right, obtuse, etc.).
    
11. 
    Cartesian coordinate system can also be for three dimensions by in­cluding a third axis - z-axis - through the origin perpendicular to the other two axes.
    
12. 
    The coordinate axes may be left-handed or right-handed, depending
    on the way positive directions are given to the axes.
    

2. 
   Match the terms from the left column and the definitions from
   

3. 
   Read and translate the sentences.
   

1. 
   Two lines are used in this system.
   
2. 
   These axes divide the plane into four quadrants.
   
3. 
   The Cartesian coordinate system was introduced in the 17th century.
   
4. 
   This particular discovery allowed the application of algebraic meth­ods to the geometry.
   
5. 
   The coordinates can be used for three dimensions.
   
6. 
   The axes may be left-handed or right-handed, depending on the way
   positive directions are given to the axes.
   
7. 
   The system is said to be an oblique coordinate system.
   

4. 
   Give the English equivalents of the following words and word combinations:
   

базисная прямая, прямоугольная координатная система, система прямоугольных (декартовых) координат, система косоугольных координат, система плоскостных декартовых координат, начало координат, квадрант, вертикальное отображение, ордината, абсцисса, левосторонняя координатная ось, вертикальная ось, горизонтальная ось.

5. 
   Read the sentences and think of a word which best fits each space.
   

1. 
   The position of a point in the ... system is determined by its distances axes.
   

1. 
   The point О of ... of two axes is the ... of the coordinate system.
   

4. 
   ... is the distance of the point from the x-axis in a direction parallel to the y-axis.
   
5. 
   The two axes divide the plane into four ....
   
6. 
   A point in Cartesian coordinates is represented by an ... of numbers
   

8.The ... in planar Cartesian coordinate system can be both at right and obtuse ... to each other.

9. Cartesian coordinate system can also be for two and three .... . Three imensions include a third axis - z-axis – through …. to the other two axes.

10. The coordinate axes may be left-handed or right-handed, depending on the way ... are given to the axes.

6. 
   Translate the paragraphs into English.
   

1. Прямые х, у, z называются координатными осями, точка их пересечения 0 - началом координат, а плоскости ху, yz, xz – координатными плоскостями.

2. В декартовой системе прямоугольных координат на плоскости каждой точке соответствует пара действительных чисел х и y,
определяющих положение данной точки на плоскости, и, наоборот,
каждой паре действительных чисел х и у соответствует только одна точка
на плоскости.

3. Координатой у точки М называется число, измеряющее расстоя­ние от данной точки до прямой Ох и взятое со знаком «плюс», если данная точка М расположена выше прямой Ох, и со знаком «минус», если точка М расположена ниже прямой Ох. Координату у называют ординатой, а ось Оу - осью ординат.

7. 
   Read and translate the following sentences. Write 2-3 special and tag questions to each of them.
   

1. 
   It is surface composed of plane polygonal surfaces.
   
2. 
   This term is used for closed solid figures.
   
3. 
   These figure played a significant part in Greek geometry.
   
4. 
   That polyhedron has identical polyhedral angles.
   

6. He used them in his complicated model.

7. These solids were known to Plato.

8. There are some possible convex regular polyhedra in this text.

9. A plane cuts other faces.

10. The vertices lie at the centers of the edges of the original cube.

8. 
   Put the words in the correct order to make the sentences.
   

1. 
   were, ancient, solids, known, Greeks, these, to.
   
2. 
   meeting, points, are, the vertex, two, there, at.
   
3. 
   a figure, formed, a polygon, three or more, is, by, points.
   
4. 
   figure, is, three-dimensional, this, a, geometric.
   
5. 
   an angle, one quarter, turn, right angle, equal to, compete, is, a, of, a.
   
6. 
   the eccentricity, the conic, of, the constant, is.
   
7. 
   central conics, the hyperbola, known, and, are, the ellipse, as.
   
8. 
   by, a, three, is, a triangle, figure, line, formed, closed, plane, seg­ments.
   

9. 
   Give the English equivalents of the following words and word combinations:
   

многогранный угол, замкнутая пространственная фигура, тело геометрически правильной формы, прямая призма, архимедово тело, кубооктаэдр, грань (плоская поверхность), антипризма, икосододекаэдр, ребро, усеченный куб, полуправильный многогранник, платоново тело восьмигранник (октаэдр), куб, четырехгранник (тетраэдр), выпуклый многогранник, вогнутый многогранник, двадцатигранник (икосаэдр), од­нородный многогранник.

10. 
    Read and decide which of the statements are true and which are false. Change the sentences so they are true.
    

1. 
   A polyhedron is a surface composed of plane triangular surfaces.
   
2. 
   The sides of the polygons, joining two faces, are its edges.
   
3. 
   There're two types of polyhedra: concave and convex ones.
   
4. 
   The faces of a regular polyhedron are formed by identical (congruent) regular polygons.
   
5. 
   A tetrahedron has got six square faces.
   
6. 
   An octahedron has got eight triangular faces.
   
7. 
   A dodecahedron has got twenty triangular faces.
   
8. 
   The five regular solids were known to Plato and so they're often
   called Platonic solids.
   
9. 
   A uniform polyhedron is a polyhedron that has identical polyhedral
   angles at all its vertices and has all its faces formed by regular polygons.
   
10. 
    An icosidodecahedron, a cuboctahedron and truncated cube represent the so called "semiregular polyhedra".
    

11. 
    Match the terms from the left column and the definitions
    

12. 
    Read the definitions and decide what terms are defined.
    

1. 
   A solid figure that has four triangular faces.
   
2. 
   One of the plane regions bounding a polyhedron.
   
3. 
   A solid figure that has six identical faces.
   
4. 
   A line joining two vertices of a geometric figure.
   
5. 
   A polyhedron that has eight faces.
   
6. 
   A polyhedron that has twelve pentagonal faces.
   

13. 
    Translate the text into English.
    

Поясним данное определение на примере куба. Куб есть выпуклый многогранник. Его поверхность состоит из шести квадратов: ABCD, BEFC, ... Они являются его гранями. Ребрами куба являются стороны этих квадратов; АВ, ВС, BE, ... . Вершинами куба являются вершины квадратов А, В, С, D, Е,... . У куба шесть граней, двенадцать ребер и во­семь вершин.

14. 
    Read and translate the following sentences. Write 2-3 special and tag questions to each of them:
    

1. 
   The given figure is formed from two congruent polygons with their
   corresponding sides parallel and the parallelograms formed by joining the cor­responding vertices of the polygons.
   
2. 
   A right prism is one in which the lateral edges are at right angles to
   the bases.
   
3. 
   One base is displaced with respect to the other, but remains parallel to it.
   
4. 
   The term "cone" is often used loosely for "conical surface".
   
5. 
   The common vertex isn't coplanar with the base.
   
6. 
   The pyramid which has its axis perpendicular to its base is a right pyramid.
   
7. 
   The given surface is composed of plane polygonal surfaces.
   
8. 
   This term is used for closed solid figures.
   
9. 
   Greeks thought that these figures played a significant part in geometry.
   

10. 
    That polyhedron has identical polyhedral angles.
    
11. 
    Other polyhedra can be generated by truncated the other regular
    polyhedron.
    
12. 
    Kepler used these solids in his complicated model.
    
13. 
    These solids were already known to Plato.
    
14. 
    The given plane cuts other faces.
    
15. 
    We see that all vertices lie at the centers of the edges of the original cube.
    

15. 
    Read the definitions and decide what terms are defined.
    

1. 
   A solid figure that has four triangular faces.
   
2. 
   One of the plane regions bounding a polyhedron.
   
3. 
   A solid figure that has six identical faces.
   
4. 
   A line joining two vertices of a geometric figure.
   
5. 
   A polyhedron that has eight faces.
   
6. 
   A polyhedron that has twelve pentagonal faces.
   

16. 
    Read and decide which of the statements are true and which are false. Change the sentences so they are true.
    

1. 
   A prism is a solid figure formed from three congruent polygons with their corresponding sides perpendicular.
   
2. 
   Prisms are named according to the base, thus, a triangular prism has two triangular bases.
   
3. 
   There're only two types of prisms: right and regular.
   
4. 
   A cone is a solid figure formed by a circle and curve on a plane and all the lines joining points of the base to a fixed point
   
5. 
   The curved area of the cone forms its lateral surface.
   
6. 
   A cone that has its axis perpendicular to its base is an oblique cone.
   
7. 
   The altitude of a cone is the line parallel to the plane of the base.
   
8. 
   A pyramid is a solid figure formed by a polygon (the base) and a number of triangles (lateral faces) with a common vertex that is coplanar with the base.
   
9. 
   A pyramid that has its axis perpendicular to its base is a right pyramid.
   

10. 
    The volume of any pyramid is l/3Ah, where A is the area of the base.
    
11. 
    The slant height of the pyramid is the altitude of a face and the total surface area of the lateral faces is l/2sp, where p is the perimeter of the base polygon.
    

17. 
    Translate the definitions of the following mathematical terms.
    

1. 
   altitude – the perpendicular distance from the base of a figure to its
   highest point or to the side parallel to the base;
   
2. 
   circular – in the shape of a circle; round;
   
3. 
   cone – a flat-based, single-pointed solid formed by a rotating straight
   line that traces out a closed-curved base from a fixed vertex point that is not in
   the same plane as the base; esp. one formed by tracing a circle from a vertex
   perpendicular to the center of the base;
   
4. 
   coplanar – in the same plane: said of figures, points, etc;
   

5. 
   generator (generatrix) – a point, line or plane, whose motion gener­ates a curve, plane, or figure;
   
6. 
   height – the distance from the bottom to the top;
   
7. 
   hexagon – a plane figure with six angles and six sides;
   
8. 
   hexagonal – having a six-sided base or section: said of a solid figure;
   
9. 
   lateral – of, at, or toward the side; sideways;
   
10. 
    parallelogram – a plane figure with four sides, having the opposite
    sides parallel and equal;
    

12. 
    quadrangle – a plane figure with four angles and four sides;
    
13. 
    rectangle – any four-sided plane figure with four right angles;
    

12. 
    slant – an oblique or inclined surface, line, direction, etc; slope; in­
    cline;
    

12. 
    triangular – of or shaped like a triangle; three-cornered;
    

12. 
    volume – the amount of space occupied in three dimensions; cubic
    contents or cubic magnitude.
    

18. 
    Translate the sentences into English.
    

1. 
   Отрезки, соединяющие вершину конуса с точками окружности
   основания, называются образующими конуса.
   
2. 
   Объем любой треугольной пирамиды равен одной трети произведения площади основания на высоту.
   
3. 
   Осью правильной пирамиды называется прямая, содержащая ее
   высоту.
   
4. 
   Ребра призмы, соединяющие вершины оснований, называются
   боковыми ребрами.
   
5. 
   Многогранником называется тело, ограниченное конечным чис­лом плоскостей,
   
6. 
   Боковая поверхность прямой призмы равна произведению пери­
   метра основания на высоту призмы.
   
7. 
   Пирамидой именуется геометрическая фигура с многоугольным
   основанием и четырьмя сторонами в виде треугольников, сходящимися в
   вершине пирамиды.
   

9. Конус – это твердое тело с одной вершиной и основанием в виде

10. Правильной считается пирамида с осью, перпендикулярной основанию.­

11. 
    Конусы, призмы и пирамиды названы по типу их оснований.
    
12. 
    Высотой конуса именуется перпендикулярное расстояние от
    его вершины до плоскости основания.
    

Высотой призмы называется расстояние между плоскостями ее оснований. Отрезок, соединяющий две вершины, не принадлежащие одной грани, называется диагональю призмы. Призма называется прямой, если ее боковые ребра перпендикулярны основаниям. В противном случае призма называется наклонной. Прямая призма называется правильной, если ее основания являются правильными многоугольниками.

1. 
   Choose the correct variant of the answer.
   

1. 
   flat angle (D) obtuse angle
   
2. 
   right angle (E) reflex angle
   
3. 
   round angle (F) acute angle
   

1. 
   parabola (D) focus
   
2. 
   hyperbola (E) transverse axis
   
3. 
   ellipse (F) circle
   

1. 
   angle (D) quadrilateral
   
2. 
   cube (E) star polygon
   
3. 
   triangle (F) square
   

1. 
   polyhedron (D) quadrilateral
   
2. 
   polygon (E) circle
   
3. 
   isosceles (F) dodecahedron
   

1. 
   curvature (D) curve
   
2. 
   straight line (E) height
   
3. 
   ray (F) circle
   

2. 
   Give the English equivalents of the following words and word combinations:
   

соответственный угол, тупоугольный треугольник, касательная ду­га, хорда, кольцо, окружность, пространство, уравнение прямой в отрез­ках, вектор положения точки, пространственная кривая, прямолинейная координата, по часовой стрелке, против часовой стрелки, угол вращения, выпуклый многоугольник, равноугольный многоугольник.

3. 
   Give the Russian equivalents of the following words and word combinations:
   

1. 
   edge;
   
2. 
   origin of coordinates;
   
3. 
   reference line;
   
4. 
   mirror image;
   
5. 
   translation of axes;
   
6. 
   generating angle;
   
7. 
   semi-regular polyhedron;
   
8. 
   truncated cube;
   
9. 
   oblique cone;
   
10. 
    slant height.
    

4. 
   Write special questions using the words in brackets.
   

1. 
   This figure is formed from two congruent polygons. (What, How many)
   

1. 
   The polyhedron has got identical polyhedral angles. (What angles)
   

4. 
   The vertices lie at the centers of the edges. (What, Where)
   
5. 
   They could be formed by different section. (What...by, What)
   
6. 
   Cavaliery had discovered this system by 1774. (Who, What system)
   

5. 
   Translate the text without using a dictionary.
   

Here, the axis of the parabola is the x-axis, the directrix is the line x = -a, and the focus is the point (a,0). The length of the chord through the focus perpendicular to the axis is equal to 4a.

The focal property (1) of the parabola is that for any point P on the curve, the tangent at P (APB) makes equal angles with a line from the focus F to P and with a line parallel to the x-axis. This is also called the reflection property (2), since for a parabolic reflector light from a source (3) at the focus would be reflected in a beam (4) parallel to the x-axis and sound (5) would be similarly reflected.
Notes:

1. 
   focal property - фокальное свойство
   
2. 
   reflection property - свойство отражения
   
3. 
   source - источник
   
4. 
   beam - луч
   
5. 
   sound – звук
   

6. 
   Use the figure for completing the following statements.
   

2. KN is twice as long as................................

3. LM is called а………………………….of а circle.

4. RL has the same length as ……………………….

5. ▲ MRN is аn................................ triangle.

6. Point R is called the ...................................of the circle and the ... ........................of ∟KRL.

7. MN is called .................................... of а circle.

8. МN is called аn ............................................

9. ∟MRN is аn...........................................аngle.

10. ∟MRK is а.......................................... angle.

11. No matter how short аn arc is, it is.................... at least slightly.

12. The term circumference means....................................

13. А diameter is а chord which................................... .

14. А circle is а set of points in а plane each of which.......................... .

15. We cannot find the circumference of а circle bу adding......................

7. 
   Translate the following sentences.
   

1. 
   Сумма углов треугольника равна 180◦.
   
2. 
   В треугольнике может быть только один тупой угол и два острых.
   
3. 
   В равностороннем треугольнике все углы равны.
   
4. 
   Углы при основании в равнобедренном треугольнике равны.
   
5. 
   В прямоугольном треугольнике сумма квадрата катетов равна квадрату гипотенузе.
   
6. 
   В прямоугольнике противоположные стороны равны и параллельны.
   
7. 
   Параллельные линии не пересекаются.
   
8. 
   При помощи циркуля можно начертить окружность.
   
9. 
   Площадь круга равна חR².
   
10. 
    Любая точка лежащая на окружности равноудалена от центра.
    
11. 
    Мы всегда можем вычислить площадь криволинейной трапеции.
    
12. 
    Синусоиду можно растянуть вдоль оси координат.
    

8. 
   Complete the sentences with the following words:
   

legs, a ray, polygon, a radius, a center, a hypotenuse, triangles, ח, a diameter, a circle, circumference, an angle, an obtuse, a chord, an acute, an equilateral.

1. 
   You certainly remember that by extending a line segment in one direction we obtain ... .
   
2. 
   The following symbol ∟ is frequently used in place of the word ... .
   
3. 
   Since PD (except for point P) lies in the exterior of ∟APB, we say that ∟APD is greater than a right angle and call it ... .
   

4. 
   A simple closed. Figure formed by line segments is called... .
   
5. 
   This is true of..... – geometric figures having three sides.
   
6. 
   ▲DEF is called .... which means that its two sides have the same measure.
   
7. 
   ▲ABC is referred as .... triangle.
   

8. 
   In ▲MKL, ∟M is the right angle sides MK and ML are called the..., and side KL is called the... .
   
9. 
   A .... is a set of points in a plane each of which is equidistant, that is the same distance from some given point in the plane called...
   
10. 
    A line segment joining any point of the circle with the center is called…. of a circle is a line segment whose endpoints are points on the circle.
    
11. 
    ….is a chord which passes through the center of the circle.
    
12. 
    Instead of speaking of the perimeter of a circle, we usually use the term... .
    
13. 
    The number c/d or c/2*r which is the same for all circles, is designated by … .