# Introduction to Geometric Construction: Angles

Geometrical construction of lines involves the use of lines and angles to depict a shape or an object.

A Line is a mark or stroke long in proportion to its breadth, made with a pen, pencil, tool, etc on a surface.

A line can also be defined as a long thin mark made by a pen, pencil, marker, etc.

Types of angles:

· Acute Angle: This is an angle less than 90º

· Obtuse Angle: this angle is greater than 90º but not more than 180º

· Reflex Angle: this angle is greater than 180º but not more than 360º

· Right Angle: this is angle 90º

· Angle on a straight line: the angle is 180º. It is also referred to as ‘straight angle’.

· Angle that makes a revolution: the angle is 360º or angle around a point. It is full rotation.

· Complementary angles are two angles with the sum of 90º

· Supplementary angles are two angles with the sum of 180º

Questions:

1. What does geometrical construction of lines involve?

2. What is a line?

3. Outline and clearly describe 5 different types of angles.

4. Outline the differences between acute, Obtuse and Reflex angles.

5. Why is 180° called a straight angle?

6. Differentiate between complimentary angles and supplementary angles.