This graph does have the symmetric shape of a cosine function and it has 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, the orientation is incorrect. Because the coefficient $\displaystyle\frac{{4}}{{3}}\usepackage{cmbright}\Huge\$ is negative, this graph should be a reflection across the x-axis compared to the orientation of $\displaystyle{y}={\cos{{x}}}\usepackage{cmbright}\Huge\$ .