Three questions kids ask

Does the order matter?No. Going from (4, 6) back to (1, 2) gives legs of −3 and −4. But (−3)² = 9 and (−4)² = 16, the same squares, because squaring a negative makes it positive. Right to left is the same length as left to right. A distance is never negative.

Why the square root?The theorem hands you c², the hypotenuse squared. Squaring and taking the square root are inverses, undo partners like adding and subtracting in Unit 1, Lesson 1. The square root undoes the squaring and gives you back the length.

Slope uses the same two numbersFrom Unit 4, slope is rise over run: the difference in y's divided by the difference in x's. Distance squares and adds the same two differences. Same legs, two different questions: how steep, and how long.