Question

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

Answer 1

I think you missed an `x` (in the argument of `cos` I think).
If it is: `y=-1/2cos(7/2x)`

The amplitude is given by the number in front of `cos`, i.e., `-1/2` ( `cos` oscillates between `1/2` and `-1/2`) while the period is given by the coefficient, `7/2`, in front of `x` as:
`7/2`=`2pi`/period;

Giving: period=`4/7pi`