Correct. The values of this function range from $\displaystyle-{3}\usepackage{cmbright}\Huge\$ to 3, so the amplitude is 3. This means $\displaystyle{a}=\pm{3}\usepackage{cmbright}\Huge\$ . Because the cosine graph has not been reflected over the x-axis, a must be positive. So $\displaystyle{a}={3}\usepackage{cmbright}\Huge\$ . Two cycles are shown over the interval $\displaystyle{\left[{0},{2}\pi\right]}\usepackage{cmbright}\Huge\$ . This implies that $\displaystyle{b}={2}\usepackage{cmbright}\Huge\$ .