Question

line ab is parallel to line cd. what is the measure of ∠4? 180° 120° 10° 100°

Explanation:

Step1: Identify corresponding angles

Since line AB is parallel to line CD, ∠4 and the angle adjacent to the 80 - degree angle (let's call it ∠6) are corresponding angles. The angle adjacent to the 80 - degree angle and the 80 - degree angle form a linear - pair.

Step2: Calculate the measure of ∠6

A linear - pair of angles sums to 180 degrees. If one angle is 80 degrees, then the other angle (∠6) is 180 - 80=100 degrees.

Step3: Determine the measure of ∠4

Because ∠4 and ∠6 are corresponding angles and corresponding angles of parallel lines are equal, ∠4 = 100 degrees.

Answer:

100°