Terms used in Geometrical Construction

TERMS USED IN GEOMETRICAL CONSTRUCTION

Important technical terms used in simple geometrical construction are recalled in this section. 

1. Point: A point is refered as a circle of zero radius. It is denoted by a small dot. 

2. Line : A line is a two dimensional figure formed by a number of points in a specified path. A line is classified into (i) Straight line and (ii) Curved line. 

A straight line is a line joining two points through the shortest path. A line generated by a point which lies in a constantly changing direction is known as curved line.

3. Angle : The inclination between two intersecting lines is known as angle. When the angle is 90° (ie. the inclination between two perpendicular lines) it is called right angle; If the angle is less than 90° it is called acute angle and if the angle is more than 90° it is called obtuse angle. 

4. Triangle : A plane figure formed by three straight lines containing three angles is known as triangle. 

If all the three angles are equal it is called equilateral triangle ; if two sides as well as the angles opposite to them are equal it is called isosceles triangle; If none of the sides or angles equal it is called scalene triangle.

5. Quadrilateral : A plane figure bounded by four straight lines is called Quadrilateral.

Parallelogram is a Quadrilateral in which the opposite sides are parallel. 

Square is a Quadrilateral in which all the sides are equal and the angles are at right angles. 

Rectangle is a Quadrilateral in which the opposite sides are equal and the angles are at right angles. 

Rhombus is a Quadrilateral in which all the sides are equal and the angles are not at right angles, but the opposite angles are equal. 

Rhomboid is a Quadrilateral in which the opposite sides are equal but angles are not at right angles to each other. 

Trapezoid is a Quadrilateral in which no side is equal to other, but may have two pairs of opposite sides parallel. It is also called as Trapezium.

6. Polygon : A plane figure bounded by more than four straight lines and containing more than four angles is known as polygon. 

A polygon having equal sides and equal angles is called a regular polygon. 

Polygons are classified according to the number of their sides and angles.

Pentagon is a polygon having five equal sides (when five sides are equal then five angles formed by these lines are also equal). 

Hexagon is a polygon having six equal sides. 

Heptagon is a polygon having seven equal sides. 

Octagon is a polygon having eight equal sides. 

Nonagon is a polygon having nine equal sides. 

Decagon is a polygon having ten equal sides. 

Undecagon is a polygon having eleven equal sides. 

Duodecagon is a polygon having twelve equal sides.

7. Circle : A plane figure bounded by a curved line generated by a point moving at equidistant from the fixed point is known as circle. 

The fixed distance from the centre to the circumference of circle is called the radius. A straight line passes through the centre and meeting the circumference at both ends is known as diameter of the circle.

A part of the circumference of circle is known as arc. 

A part of a circle bounded by an arc and two radii is called sector of a circle.

A straightline joining any two points on the circumference is known as Chord of a circle. Half the portion of a circle is known as semicircle. 

A straightline which touches the circumference of the circle but does not cut the circle is known as Tangent to a circle.