Question

5/2 cos x/2 what is the amplitude and period?

Answer 1

The amplitude is the highest the function ever gets.  That happens when the
cosine is ' 1 '.  At that point, the value of the function is  5/2 .

The period is the first time after zero that the angle in the cosine is  2π .

                                            x/2 = 2π

Multiply each side by  2 :    x = 4π

The period is  4π .