Page 42 - Mathematics Class - IX

5. Complementary angles: Two angles whose sum is 90°.

6. Supplementary angles: Two angles whose sum is 180°.

7. Adjacent angles: Two angles are adjacent, if they have a common vertex, a common arm and their non-
common arms are on different sides of the common arm.

A
D

B C

Fig. (b): Adjacent angles

8. Linear pair of angles: A pair of adjacent angles is said to form a linear pair of angles, if their non-common
arms form a straight line.

D

A B C

Fig. (c): Linear pair of angles

9. Vertically opposite angles: These are formed when two lines, say AB and CD, intersect each other, say at
the point O.

D
A

O

B
C

Fig. (d): Vertically opposite angles

40