Simplify -cos(x)^2-sin(x)^2

$- \cos^{2} (x) - \sin^{2} (x)$

Factor $- 1$ out of $- \cos^{2} (x)$ .

$- (\cos^{2} (x)) - \sin^{2} (x)$

Factor $- 1$ out of $- \sin^{2} (x)$ .

$- (\cos^{2} (x)) - (\sin^{2} (x))$

Factor $- 1$ out of $- (\cos^{2} (x)) - (\sin^{2} (x))$ .

$- (\cos^{2} (x) + \sin^{2} (x))$

Rearrange terms.

$- (\sin^{2} (x) + \cos^{2} (x))$

Apply pythagorean identity.

$- 1 \cdot 1$

Multiply $- 1$ by $1$ .

$- 1$