This has the right amplitude and period, and it is the graph of a cosine function. However, it has been flipped over the x-axis, which is what would happen if there was a negative coefficient. In particular, it passes through

$\displaystyle{\left({0},-\frac{{3}}{{2}}\right)}\usepackage{cmbright}\Huge\$ , while the graph of $\displaystyle{y}=\frac{{3}}{{2}}{\cos{{4}}}{x}\usepackage{cmbright}\Huge\$ would pass through $\displaystyle{\left({0},\frac{{3}}{{2}}\right)}\usepackage{cmbright}\Huge\$ .