All angles in this diagram are 51 or 129. See below for a specific angle.
Step-by-step explanation:
Parallel lines cut by a transversal have specific angle relationships.
Alternate Interior Angles are angles across the transversal between pairs of parallel lines. These angles are congruent. Example: 3, 6, 7, and 10 are all congruent and are pairs of alternate interior angles. 4, 5, 8, and 9 are congruent as well.
Alternate Exterior Angles are angles across the transversal outside of the parallel lines. These angles are congruent. Example 2 & 11 are congruent alternate exterior angles. 1 and 12 are another set.
Supplementary angles are angles which form a line and add to 180. If angle 1 + angle 2 = 180 and angle 2 = 129, then Angle 1+ 129 =180. Angle 1 must be 51 degrees.
Vertical angles are angles across a vertex. They are congruent. Example: Angle 2 and Angle 3 are both 129.
Using these relationships, the following angles have the following measures:
