Question

How do alternate interior angles occur?

Answer 1

Alternate interior angles occur when a transversal (a line) cuts through two other parallel lines.

Here, the parallel lines are `m` and `n` and the transversal is `l`.

The alternate interior angles are located in pairs: `angle4,angle8` is a pair and `angle1,angle5` is a pair.

Alternate interior angles are located on opposite sides of the transversal and on the other parallel line. Both are on the interior of the two parallel lines.

Alternate interior angles are always congruent: that is, `angle1cong angle5` and `angle4congangle8`.

By the definition of congruence, we can also say that `mangle1=mangle5` and `mangle4=mangle8`.