Right triangles ABD and CDB share a hypotenuse, segment DB. The shared hypotenuse should clue you to use the Pythagorean theorem. See that w and x are lengths of the legs of right triangle ABD; side AD has length w, side AB has length x. Also, y and z are lengths of the legs of right triangle CDB; side CD has length z, side CB has length y. Where a and b are lengths of the legs of a right triangle, and c is the length of the hypotenuse, a2+b2 = c2. So here w2+x2 = length BD2; y2+z2 also equals length BD2. The quantities are equal, and the answer is (C).