Answer
The sine function is not one-to-one over its whole domain
Work Step by Step
The function $f(x)=\sin x$ is not an one-to-one function over its whole domain, therefore in order for the function to have an inverse we must restrict the domain so that the function is one-to-one.
For example the domain might be $\left[-\dfrac{\pi}{2},\dfrac{\pi}{2}\right]$.
