Find the value of $x = \sin^2 \varphi - \cos^2 \varphi$ if $\varphi$ is $\pi / 4$ or $45^\circ$.

Find the value of $x = \sin^2 \varphi - \cos^2 \varphi$ if $\varphi$ is $\pi / 4$ or $45^\circ$.

A. 3 C. 1
B. 2 D. 0