Answer
We would use the indirect method to prove (a), (b), and (e)
Work Step by Step
(a) Let $~~m\angle A \gt m\angle B$
Assume that $AC = BC$
This would lead to a contradiction.
We would prove this statement with the indirect method.
(b) Suppose these two exterior angles are not congruent.
Assume that $l$ is parallel to $m$
This would lead to a contradiction.
We would prove this statement with the indirect method.
(c) We would prove this statement directly.
(d) We would prove this statement directly.
(e) Assume that perpendicular bisectors of a line segment are not unique.
This would lead to a contradiction.
We would prove this statement with the indirect method.
