# RD Sharma Solutions for Class 9 Maths Chapter 8: Lines and Angles

The very basics of geometry are Lines & Angles. In this chapter, we will learn about various types of lines and angles.

A line is a representation of a set of points when they are joined. A line is always one-dimensional and does not have any thickness. It is also defined as the shortest distance between 2 points. In this chapter, you'll be entertained with several types of lines that are important to understand various concepts in higher standards. A vertical line is a line that goes from up to down, and horizontal lines go from right to left or vice-versa. Perpendicular lines are lines that intersect each other at an angle of 90°. Finally, parallel lines are 2 lines when the distance between them is equal everywhere, and they are supposed to meet at infinity.

An Angle is defined as a figure of 2 straight lines joining at a point. The symbol ∠ represents the angle. There are several types of angles that we will learn in this chapter, A complementary angle is a set of 2 angles when their sum is 90°. For example, the complementary angle of a 20° angle is (90 – 20 = 70) 70°. On the other hand, a Supplementary Angle is a set of 2 angles when they add up to 180°. For example, the supplementary angle of a 120° angle is (180 – 120 = 60) 60°.

An Acute Angle is when the measurement of the angle is less than 90°.

When 2 lines join each other at 90°, then the angle formed is called a Right Angle.

If the value of the angle is more than 90° but less than 180°, then the angle is called Obtuse Angle.

A Reflex Angle is the larger angle when the angle is more than 180° but less than 360°.

The chapter also talks about the theorems and axioms related to the angles. There is also the mention of linear pairs, vertically opposite angles, angles made by the intersection of two parallel lines by a transversal.