# How do you determine the amplitude and period for y = -2/4 cos (7/2)?

I think you missed an $x$ (in the argument of $\cos$ I think).
If it is: $y = - \frac{1}{2} \cos \left(\frac{7}{2} x\right)$
The amplitude is given by the number in front of $\cos$, i.e., $- \frac{1}{2}$ ( $\cos$ oscillates between $\frac{1}{2}$ and $- \frac{1}{2}$) while the period is given by the coefficient, $\frac{7}{2}$, in front of $x$ as:
$\frac{7}{2}$=$2 \pi$/period;
Giving: period=$\frac{4}{7} \pi$