This graph does have the correct amplitude. However, it does not have the correct period. Remember that the period of $\displaystyle{y}={a}{\cos{{b}}}{x}\usepackage{cmbright}\Huge\$ is given by $\displaystyle\frac{{{2}\pi}}{{\left|{b}\right|}}\usepackage{cmbright}\Huge\$ .

Also notice that this is the graph of a sine function. Remember that the graph of a cosine function does not pass through the origin, and is symmetric.