You may have worked with the angle $\displaystyle\frac{{{3}\pi}}{{4}}\usepackage{cmbright}\Huge\$ , which is in the second quadrant. However, $\displaystyle\frac{{{5}\pi}}{{4}}\usepackage{cmbright}\Huge\$ is in the third quadrant and intersects the unit circle at the point $\displaystyle{\left(-\frac{\sqrt{{2}}}{{2}},-\frac{\sqrt{{2}}}{{2}}\right)}\usepackage{cmbright}\Huge\$ .