Answer:
(C)Determine the principal square root of both sides of the equation.
Step-by-step explanation:
Given: Isosceles right triangle XYZ (45°–45°–90° triangle)
To Prove: In a 45°–45°–90° triangle, the hypotenuse is
times the length of each leg.
Proof:

Because triangle XYZ is a right triangle, the side lengths must satisfy the Pythagorean theorem, 
Since a=b in an isosceles triangle:

Therefore, the next step is to Determine the principal square root of both sides of the equation.