### Home > CC4 > Chapter 1 > Lesson 1.2.1 > Problem 1-42

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. | b. | c. |

∠

*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.