It appears that you found the value of $\displaystyle{\sin{{\left(\frac{{{5}\pi}}{{3}}\right)}}}\usepackage{cmbright}\Huge\$ . Perhaps you made a mistake when converting from radians to degrees or finding the reference angle. You need to multiply a radian measure by $\displaystyle\frac{{{180}}^{\circ}}{\pi}\usepackage{cmbright}\Huge\$ to convert to degrees. So $\displaystyle\frac{{{7}\pi}}{{4}}\usepackage{cmbright}\Huge\$ radians equals $\displaystyle{{315}}^{\circ}\usepackage{cmbright}\Huge\$ and the reference angle is $\displaystyle{{45}}^{\circ}\usepackage{cmbright}\Huge\$ . Find the y-coordinate of the point where $\displaystyle{{315}}^{\circ}\usepackage{cmbright}\Huge\$ intersects the unit circle. The correct answer is: $\displaystyle-\frac{\sqrt{{2}}}{{2}}\usepackage{cmbright}\Huge\$