Question

There are two are parallel vertical lines l and m intersected by another line t making angles 1 and 3 with l and 5 and 7 with m. 1 and 4 and 2 and 3 are opposite angles at the point of intersection of l and t. 5 and 8 and 6 and 7 are opposite angles at the point of intersection of m and t. If m∠2 = 120°, what is m∠7?

Answer 1

Since lines l and m are parallel, we know that angles 1 and 5 are corresponding angles and are therefore congruent. Also, angles 4 and 8 are corresponding angles and are congruent.

We also know that angles 1 and 4 are vertical angles, so they are congruent, and angles 2 and 3 are vertical angles, so they are congruent.

Thus, we can set up the following equation:

m∠7 = m∠8 - m∠5 = m∠4 - m∠5

We are given that m∠2 = 120°, so we can use this to find m∠1:

m∠1 + m∠2 = 180° (since angles 1 and 2 are supplementary)

m∠1 + 120° = 180°

m∠1 = 60°

Since angles 1 and 5 are congruent, we know that m∠5 = 60°.

We are also given that angles 1 and 3 are complementary, so we can use this to find m∠3:

m∠1 + m∠3 = 90°

60° + m∠3 = 90°

m∠3 = 30°

Now we can find m∠4:

m∠1 + m∠4 = 180° (since angles 1 and 4 are supplementary)

60° + m∠4 = 180°

m∠4 = 120°

Finally, we can use these values to find m∠7:

m∠7 = m∠4 - m∠5

m∠7 = 120° - 60°

m∠7 = 60°

Therefore, m∠7 is 60°.