The first step of an indirect proof is to assume the opposite, or negation, of the given statement.
Assume temporarily that alternate exterior angles are not congruent.
Practice makes perfect
The first step of an indirect proof is to assume the opposite, or negation, of the given statement. Let's think about the second part of the given statement.
Alternate exterior angles are congruent.
To write a negation of this statement, we need to consider how to say its opposite. Typically this can be done using the word not.
Negation:
Alternate exterior angles are not congruent.
Since the first step is to temporarily assume the opposite, we should include this fact in our sentence.
First step:
Assume temporarily that
alternate exterior angles are not congruent.
