Alternate Interior Angles

Definition of Alternate Interior Angles

Alternate interior angles are two congruent interior angles that lie on different parallel lines and on opposite sides of a transversal.

Examples of Alternate Interior Angles

    In the figure shown, l is the transversal that cut the parallel lines. Angles a and d and angles b and c are alternate interior angles.
    example of Alternate Interior Angles

Video Examples: Alternate Interior Angles


Solved Example on Alternate Interior Angles

Ques: Find the measure of angle m in the figure shown.

    example of Alternate Interior Angles
    Choices:
    A. 120
    B. 180
    C. 60
    D. Insufficient information
    Correct Answer: C

Solution:

    Step 1: 120 + n = 180 [Straight angle.]
    Step 2: n = 60 [Solve for n.]
    Step 3: n = 60 implies m = 60, because m and n are alternate interior angles and so they are congruent.