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)