Consider an isosceles triangle. The three lines you need are the ones containing the base and the two legs.
See solution.
Practice makes perfect
Let's begin by writing the given statement.
If lines p and m are cut by a transversal t so that consecutive angles are congruent, then lines p and m are parallel and t is perpendicular to both lines.
We want to prove this statement wrong, so let's try to find a counterexample. Consider an isosceles triangle.
To get the situation described in the given statement, we will extend the base and the legs of the triangle above.
