Recall what you learned about angle relationships in previous courses. (See the Math Notes box in this lesson if you need a reminder.) Determine the measures of the labeled angles. The double arrowheads indicate that the pair of lines is parallel. Homework Help ✎
All three of these can be solved using multiple techniques related to parallel lines.
∠a: Corresponding angle with 123°, so m∠a = 123°.
∠b: ∠a and ∠b are vertical angles, so they have equal measures. Therefore, m∠b = 123°.
∠c: ∠c and 123° form a pair of supplementary angles, so m∠c = 57°.
∠f and 82° form a pair of supplementary angles. How are ∠e and ∠f related?
Since there are parallel lines, look for relationships between pairs of angles such as alternate interior, corresponding, or same-side interior.