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

- Acute angle : 0
^{o}∠ Angle ∠ 90^{o} - Right Angle : Angle= 90
^{o} - Obtuse Angle : 90
^{o}∠ Angle ∠ 180^{o} - Straight Angle : Angle = 180
^{o} - Reflex angle : 180
^{o}∠ Angle ∠ 360^{o}

**Complimentary & supplementary Angles:**

2 angles whose sum is 90^{o} are called Complimentary Angles.

2 Angles whole sum is 180^{o} 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 180^{o} 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.

.