Answer
$$\cos(-x)=\cos x$$
$\text{E}$ is the answer.
Work Step by Step
$$\cos(- x)$$
According to the Negative-Angle Identities, we have
$$\cos(-\theta)=\cos\theta$$
Therefore, $$\cos(-x)=\cos x$$
which means we would pick $\text{E}$ as the answer here.