Given that you don't provide a graph, I will try to solve this problem using the data written in the question. A cosine function is given by the formula:
[tex]y=Acos(\omega x) \\ \\ where \ A \ is \ the \ amplitude \ and \ \omega \ is \ the \ angular \ frequency[/tex]
According to the statement, the amplitude of this function is equal to [tex]3[/tex]. So we need to find the period that is related to [tex]\omega[/tex] like this:
[tex]\omega=\frac{2 \pi}{T} \\ \\ \therefore \omega=\frac{2 \pi}{\frac{\pi}{4}}=8 \ rad/seg[/tex]
 Accordingly:
[tex]y=3cos(8x)[/tex]
So this graph is shown in the figure below. The frequency of this function is 8 times the frequency of the function [tex]cos(x)[/tex] and the amplitude acts as a scaling factor.
