The graph does have the shape of a sine function, and you found the correct amplitude, but the period is incorrect. Perhaps you observed that the graph has 3 cycles and used this to choose your answer. But note that these 3 cycles are shown on the interval $\displaystyle{\left[{0},{3}\pi\right]}\usepackage{cmbright}\Huge\$ . There are only 2 cycles on the interval $\displaystyle{\left[{0},{2}\pi\right]}\usepackage{cmbright}\Huge\$ .