This graph has the correct amplitude and period, but it is the graph of a sine function. In particular, this graph passes through $\displaystyle{\left({0},{0}\right)}\usepackage{cmbright}\Huge\$ , while the graph of $\displaystyle{y}=-{3}{\cos{{\left(\frac{{1}}{{2}}{x}\right)}}}\usepackage{cmbright}\Huge\$ does not.