If two parallel lines are cut by a transversal, then each pair of alternate interior angles are
a. congruent
b. supplementary

Dear Student,


In the figure above, Line l and m are parallel to each other and is cut by traversal n.

angle 1 and angle 4 are pair of alternate interior angle

$$\begin{gathered} \angle 1 + \angle 2 = 180° ..............eq 1(Linear pair of angle) \\ \angle 4 + \angle 2 = 180° .............eq 2(sum of interior angles on the same side of traversal is 180°) \\ from eq 1 and eq 2, we get, \\ \angle 1 = \angle 4 \end{gathered}$$
Here we can see that alternate interior angles are equal or congruent.​​​​​​

Regards,