I'll use x instead of theta
(sin(x) - cos(x)) - (sin(x) + cos(x))^2
(sin(x) - cos(x)) - (sin^2(x) + 2*sin(x)*cos(x) + cos^2(x))
(sin(x) - cos(x)) - (sin^2(x) + cos^2(x) + 2*sin(x)*cos(x))
(sin(x) - cos(x)) - (1 + 2*sin(x)*cos(x))
sin(x) - cos(x) - 1 - 2*sin(x)*cos(x)
- 2*sin(x)*cos(x) - cos(x) + sin(x) - 1
The final answer is choice D
