## Precalculus (6th Edition)

When we see $x^{2}$ in the function expression, our first thought should be "this is probably not one-to-one", because, for example, $1^{2}=(-1)^{2}$... $f(x)=\sqrt{36-x^{2}}$is defined for $x=1$ and $x=-1,$ (different values from the domain ...) $f(1)=\sqrt{35}=f(-1)$ ( ... have the same function value)