This is a 45-45-90 triangle. The side facing the 90 degree angle would be the a square root 2. The sides facing the 45 degree angles would be a. 2 square root 2 is facing a 45 degree angle, so that means the side facing the 90 degree angle would be 2 square root 2 x square root 2 which is 4. Basically: a = 4 b = 2 square root 2
