[My previous solution had some lettering that did not match the drawn figure. I think I have corrected all the errors below.]Draw lines CR and RB so that ΔCRB ≅ ΔCPA Now draw in QR: You can finish now. It's mostly corresponding parts of congruent triangles and the Pythagorean theorem. Here are some of the steps: ΔCRB ≅ ΔCPA BR = AP ∠ACP = ∠BCR ∠ACP + ∠PCQ + ∠QCB = 90° ∠ACP + 45° + ∠QCB = 90° ∠ACP + ∠QCB = 45° ∠BCR + ∠QCB = 45° Show that ΔQCP ≅ ΔQCR Then PQ = QR ≅QBR is a right triangle BR² + BQ² = QR² AP² + BQ² = PQ² If you have trouble finishing, tell me in the space below, and I'll get back to you be email. (No charge, ever!!) Edwin