- Adjacent Angles:
Two angles in a planes are called adjacent angles, if they have a common vertex, a common side, and their interiors do not have a common point.
Ð1 and Ð2 below are adjacent angles.
- Congruent Angles:
Angles having the same measure are called congruent angles. The two marked angles in the following isosceles triangle are congruent angles and Ðd and Ðe are congruent.
- Linear Pair of Angles:
A pair of adjacent angles formed by intersecting lines is called a Linear Pair of Angles.
In the following picture, Ð1 & Ð2, Ð2 & Ð4, Ð3 & Ð4, and Ð3 & Ð4 are linear pairs.
- Vertically Opposite Angles:
When two lines intersect, then the angles that are opposite one another at the intersection are called Vertically Opposite Angles. The measures of the vertically opposite angles are equal.
In the above picture, Ð1 & Ð4, and Ð2 & Ð3 are vertically opposite.
Directions: Answer the following questions. Also draw all the above kinds of angles, measure them using protractor and label them.