Use the horizontal line test.
If any 2 points along the curve of F(x) touch a horizontal line, then the inverse is NOT a function.
This is because if 2 points share the same 'y' value in F(x), then they would share the same 'x' values in the inverse function. This is not allowed for a function.
For the given curve, it passes the horizontal line test. Therefore the inverse IS a function.
