When two line segments or lines meet at a common point, at the point of intersection an angle is formed. When a ray is rotated about its end point, then the measure of its rotation in an anti-clockwise direction is the angle formed between its initial and final position.

In fig. 1 if the ray \(\small \overrightarrow{OP}\)

Let us now have a look at complementary angles and supplementary angles.

**Complementary Angles**

When the sum of two angles is 90°, then the angles are known as **complementary angles**. In other words, if two angles add up to form a right angle, then these angles are referred to as complementary angles.

In Fig. 2 given above, the measure of angle BOD is 60^{o} and angle AOD measures 30^{o}. On adding both of these angles we get a right angle, therefore ∠BOD and ∠AOD are complementary angles.

The following angles in Fig. 3 given below are complementary to each other as the measure of the sum of both the angles is 90^{o}. ∠POQ and ∠ABC are complementary and are called **complements** of each other.

**Supplementary Angles**

When the sum of two angles is 180°, then the angles are known as supplementary angles. In other words, if two angles add up to form a straight angle, then these angles are referred to as **supplementary angles**.

In Fig. 4 given above, the measure of ∠AOC is 60^{o} and ∠AOB measures 120^{o}. On adding both of these angles we get a straight angle. Therefore, ∠AOC and ∠AOB are supplementary angles, and both of these angles are known as a supplement of each other.

**Complementary angles and Supplementary angles differences:**

How could remember easily the difference between Complementary angle and supplementary angles?

- “
**C**“**letter of****C**omplementary stands for “**C**orner” (A right angle, \(90^{\circ}\)) - “
**S**“**S**upplementary stands for “**S**traight” ( a straight line, \(180^{\circ}\)))

‘