5. You have m∠1 = 90° = m∠2, so it is reasonable to invoke the transitive property. (Step 4 would use "angles with the same measure are congruent" to complete the proof.)
6. The difference in x-coordinates is (4-1) = 3. The difference in y-coordinates is (22-9) = 13. By the Pythagorean theorem, the distance between the points is ...
