Question

Think About a Plan Write an indirect proof.
Proof
Given: 41 42
Prove:
p
• What assumption should be the first step of your proof?
. In the figure, what type of angle pair do 21 and 22 form?

Answer 1

1) Either $\ell \parallel p$ or $\ell$ ∦ $p$ (only two possibilities)

2) Assume $\ell \parallel p$ (one of two possibilities)

3) $\angle 1 \cong \angle 2$ (if two parallel lines are cut by a transversal, the corresponding angles are congruent)

4) But $\angle 1$ is not congruent to $\angle 2$ (given)

5) So $\ell$ ∦ $p$ (only other possibility)