Question

If a and b the maximum and minimum values of the function f(x) = 5 - 3 cos x, compute ab.
A) 12
C) 15
D) 16
E) None

Answer 1

cosx has values from -1 to +1, so the values of -3cosx will be between -3 and 3
so f(x) falls between 5 + 3 or 5 - 3, or
2 ≤ f(x) ≤ 8
so if a = 8 and b = 2
ab = 16