Question 1075360
Without being able to easily draw,
Make two parallel lines cut by a transversal.
Let the alternate interior angles be a and b.  They are equal.
Let angle c be an interior angle on the same side as angle a.
Let angle d be a corresponding angle to angle a
Angle d is supplementary to angle c
Angles b and d by definition are vertical angles 
Therefore angle d equals angle b and by extension to angle a.