You may have tried to use the identity $\displaystyle{\sin{{\left(\theta+{2}\pi\right)}}}={\sin{\theta}}\usepackage{cmbright}\Huge\$ to simplify $\displaystyle{\sin{{\left(\frac{{{17}\pi}}{{4}}\right)}}}\usepackage{cmbright}\Huge\$ , but made an error. First rewrite it as $\displaystyle{\sin{{\left({4}\pi+\frac{\pi}{{4}}\right)}}}\usepackage{cmbright}\Huge\$ , then apply the identity twice.