We write $\displaystyle{{\cos{{45}}}}^{\circ}=\frac{{1}}{\sqrt{{2}}}\usepackage{cmbright}\Huge\$ to mean that the cosine of the angle $\displaystyle{{45}}^{\circ}\usepackage{cmbright}\Huge\$ is equal to $\displaystyle\frac{{1}}{\sqrt{{2}}}\usepackage{cmbright}\Huge\$ .

We can express this same relationship another way using an inverse function, where the input and the output are reversed. The $\displaystyle-{1}\usepackage{cmbright}\Huge\$ is used here to indicate an inverse function. So we write $\displaystyle{{\cos}}^{{-{1}}}\text{}\frac{{1}}{\sqrt{{2}}}={{45}}^{\circ}\usepackage{cmbright}\Huge\$ to mean the angle whose cosine equals $\displaystyle\frac{{1}}{\sqrt{{2}}}\usepackage{cmbright}\Huge\$ is $\displaystyle{{45}}^{\circ}\usepackage{cmbright}\Huge\$ .