Question

Lines l and k are parallel to each other. A=120 degrees. and C=80 degrees. What is the number of degrees in B??

100 points

Answer 1

B = 160°

Explanation:

This is how I solved it (I hope the explanation isn't too confusing):

Since L and K are parallel, I drew a straight line from A to B. By doing this, I'm making a triangle: ΔABC

Then I solved for the angles of the triangle. First, we are given that ∠C = 80° and ∠A = 120°. Although, when I drew the vertical line from A to B, it made a 90° (see attachment).

So what we basically did was break ∠A into two parts: an angle inside ΔABC and one outside. To find the interior angle, simply subtract 90° from 120° to get 30°.

There are 180° in a triangle, so add the two interior angles you know:

30° + 80° = 110°

Then subtract 110° from 180° to find the final interior angle which is:

180° - 110° = 70°.

To find the measure of angle B, you must add all of the parts together, so the 90° outside angle and the 70° interior angle:

90° + 70° = 160°