Some functions that aren't invertible can be made invertible by restricting their domains. For example, the function x^2 is invertible if we restrict x to the interval [0inf), or to any subset of that interval. In that case, the inverse function is sqrt(x). (We could also restrict to the domain (-inf,0], in which case the inverse function would be -sqrt(x).) Similarly, by restricting the domain of the function f(x) = 2x^2 - 4x - 9 to an interval, we can make it invertible. What is the largest such interval that includes the point x = 0?
