The graph of $\displaystyle{y}={\cos{\theta}}\usepackage{cmbright}\Huge\$ has a valley from $\displaystyle\theta=\frac{\pi}{{2}}\usepackage{cmbright}\Huge\$ to $\displaystyle\theta=\frac{{{3}\pi}}{{2}}\usepackage{cmbright}\Huge\$ . Therefore, the function has negative values in this interval. So it cannot have the value $\displaystyle\frac{\sqrt{{2}}}{{2}}\usepackage{cmbright}\Huge\$ at $\displaystyle\theta=\frac{{{3}\pi}}{{4}}\usepackage{cmbright}\Huge\$ . Therefore, $\displaystyle{\left(\frac{{{3}\pi}}{{4}},\frac{\sqrt{{2}}}{{2}}\right)}\usepackage{cmbright}\Huge\$ is not on the graph of $\displaystyle{y}={\cos{\theta}}\usepackage{cmbright}\Huge\$ .