# Classifying angles

**Straight angle** is a straight line. It has measure 180°

At the picture angle ABC is straight angle

**Right angle** is half of straight angle.
It has measure 90 °

At the picture angle DEF is right angle.

**Acute angle** is less than straight angle. It has measure less than 90°

At the picture angle LMN is **acute angle**.

**Obtuse angle** is bigger than straight angle and less than straight angle. It has measure bigger than 90° and less than 180°.

At the picture angle XYZ is **obtuse angle**.

**Reflex angle** is bigger than straight angle. It has measure bigger than 180°

#### Angle pairs

**Adjacent angles** are called angles like a and
d, or a and b or
b and c or c
and d
Sum of adjacent angles are equal to straigth angle(180°), so
a = c and b = d.

**Vertical angles** are a and c
or b and d. **Vertical pair of angles are equal** i.e. a = c and b = d

Let's have two parallel lines intersected by third line.
Angles m and q or n and r or o and s
or p and t are called **corresponding**. They have the same measure.