In the figure, lines 1, m, and n are parallel. a classmate says you can use the corollary to the side-splitter theorem to find x. explain your classmate's error.

Your classmate incorrectly identified the sides that are proportional in the side-splitter theorem.

In this theorem, the segments formed on the traversal are proportional. However, in the diagram your friend is trying to prove that segments on the parallel lines are proportional. If he wanted to do that, he would need to have a different plan.