|Class 9 Maths Lines and Angles||Angles|
Angle: Angle is formed when 2 rays originate from same end point. Rays that forms angle are called arms (AB & AC are the arms in figure below) & the endpoint is called vertex. A is the vertex in figure below.
Types of Angles
Complimentary & supplementary Angles:
2 angles whose sum is 90o are called Complimentary Angles.
2 Angles whole sum is 180o are called Supplementary Angles.
Adjacent Angles: Two angles are said to be adjacent if they have a common vertex, a common arm & their non common arm are on different sides of common arm. In the figure below, ∠ ABC & ∠ DBC are adjacent angles. Ray BD us their common arm & point B is their common vertex. Ray BA & BC are non common arm.
Linear Pair of Angles: Supplementary Adjacent angles are called Linear Pair of Angles. Or, two adjacent angles whose sum is 180o are called Linear Pair. Non common arm forms a line. In figure above PQR forms straight line.
Vertically Opposite Angle: Two lines intersect itself each other at some point O, forms 2 pairs of vertically opposite angles. In the figure below ∠ AOC = ∠ BOD & ∠ AOD =∠ BOC. These are 2 pair of vertically opposite angles.