We write $\displaystyle{{\sin{{30}}}}^{\circ}={0.5}\usepackage{cmbright}\Huge\$ to mean that the sine of the angle $\displaystyle{{30}}^{\circ}\usepackage{cmbright}\Huge\$ is equal to 0.5.

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{{\sin}}^{{-{1}}}{0.5}={{30}}^{\circ}\usepackage{cmbright}\Huge\$ to mean the angle whose sine equals 0.5 is $\displaystyle{{30}}^{\circ}\usepackage{cmbright}\Huge\$ .