This graph has the shape of a cosine function and has the correct amplitude and period. However, it does not match $\displaystyle{y}=-\frac{{1}}{{3}}{\cos{{3}}}{x}\usepackage{cmbright}\Huge\$ because it does not take into account the effect of the negative sign. It should be reflected around the x-axis. The correct answer is the graph passing through $\displaystyle{\left({0},-\frac{{1}}{{3}}\right)}\usepackage{cmbright}\Huge\$ .