You may have miscalculated the effect of the $\displaystyle+\frac{\pi}{{2}}\usepackage{cmbright}\Huge\$ on the graph of cosine. It will shift the graph of $\displaystyle{y}={\cos{\theta}}\usepackage{cmbright}\Huge\$ to the left by $\displaystyle\frac{\pi}{{2}}\usepackage{cmbright}\Huge\$ units. So the graph of $\displaystyle{y}={\cos{{\left(\theta+\frac{\pi}{{2}}\right)}}}\usepackage{cmbright}\Huge\$ will have a hill just to the left of the y-axis, and a valley just to the right. This does not match the given graph.