# How do you find the amplitude and period of a function y=3 cos x?

The amplitude is 3, the period is 2$\pi$ and (if you cared) the phase change is (0, 0).
The equation can be written as $a \cos \left(b \left(x - c\right)\right) + d$. For sin and cos (but not tan) $| a |$ is the amplitude, $\frac{2 \pi}{|} b |$ is the period, and $c$ and $d$ are the phase shifts. $c$ is the phase shift to the right (positive $x$ direction) and $d$ is the phase shift up (positive $y$ direction). Hope this helps!