Graph of the Cosine Function $y = \cos x$

$y = \cos x$ is the $x$-coordinate of a point on the unit circle. Its period is $2\pi$ and its range is $-1 \leq y \leq 1$.

It is an even function, symmetric about the $y$-axis, reaching its maximum of $1$ at $x = 0$. Since $\cos x = \sin\left(x + \dfrac{\pi}{2}\right)$, it is the sine curve shifted to the left by $\dfrac{\pi}{2}$.