Question

Identify the maximum and minimum values of the function y = 3 cos x in the interval [-2π, 2π].

Answer 1

3cosx has period 2pi, (just like cosx).
The domain here is 2 periods, so we can be sure there are min and max values.
cosx has values between -1 and 1, with -1 and 1 as min and max values.

Now ask yourself this question: what is the effect of the factor 3 on this?

Answer 2

maximum value is 3 and minimum is -3
because maximum and minimum of cosx is 1 and -1.