Use a doubleangle identity to find the exact value of the ex

Use a double-angle identity to find the exact value of the expression. cos^2 135 degree - sin^2 135 degree cos^2 135 degree - sin^2 135 degree (Simplify your answer, including any radicals. Use integers or fractions for any numbers in the expression.)

sin^2 x + cos^2 x = 1
cos^2 x - sin^2 x = cos 2x

cos^2 135 - sin^2 135 = cos(2*135) = cos(270) = cos(180 + 90) = 0