Answer:
(C) y= 3cos(4x),
Explanation:
When x=0, y=3. If we substitute x into the given equations, the possible answers are A,C or D.
Lets take C, y= 3cos(4x), and substitute x=π/2.
y= 3cos(4x) = 3cos(4*π/2)=3cos(2π)=3*1=3
This agrees with our graph. Choices B and D give wrong answers.