Correct. The values of this function range from $\displaystyle-{2}\usepackage{cmbright}\Huge\$ to 2, so the amplitude is 2. This means $\displaystyle{a}=\pm{2}\usepackage{cmbright}\Huge\$ . Because the cosine graph has been reflected over the x-axis, a must be negative. So $\displaystyle{a}=-{2}\usepackage{cmbright}\Huge\$ . One cycle is shown over the interval $\displaystyle{\left[{0},\frac{{{2}\pi}}{{3}}\right]}\usepackage{cmbright}\Huge\$ . This implies that $\displaystyle{b}={3}\usepackage{cmbright}\Huge\$ .