### Theory:

Alternate interior angles:

The region between the two lines $$m$$ and $$n$$ are known as interior regions and the located in this region called interior angles.

Now observe the above diagram, there each of pair of angles named $$∠a$$ and $$∠b$$, $$∠c$$ and $$∠d$$ are marked on the opposite side of the transversal line $$l$$ and are lying between lines $$m$$ and $$n$$ are called alternate interior angles.
The each pair of alternate interior angles are equal, only when a transversal cuts the two parallel lines.
Alternate Exterior angles:

In the above diagram, we can notice each pair of angles named $$∠1$$ and $$∠7$$, $$∠2$$ and $$∠8$$ are marked on the opposite side of the transversal line $$l$$ and are lying outside of the lines $$m$$ and $$n$$ are called alternate exterior angles.
The each pair of alternate exterior angles are equal, only when a transversal cuts the two parallel lines.