For this question, you are going to need the following trig identities.
sin(3x) = 3 sin(x) - 4 (sin(x))^3
cos(3x) = 4 (cos(x))^3 - 3cos(x)
Consider the function
f(x) = 23sin(x) + 3sin(3x)
Find the maximum value attained by the function f on the whole real line.