It appears that you divided by $\displaystyle{{180}}^{\circ}\usepackage{cmbright}\Huge\$ . To convert from degrees to radians, multiply the degree measure by $\displaystyle\frac{\pi}{{{180}}^{\circ}}\usepackage{cmbright}\Huge\$ . The correct answer is $\displaystyle\frac{{{7}\pi}}{{6}}\usepackage{cmbright}\Huge\$ .