I presume you are using a calculator to determine this because otherwise this is a Calculus problem.

If you have anything in the TI series this should do for you.

Graph the function. Look at the toolbar above. There should be a "Math" option or something like it. (On the TI-92 it is F5.) Under that menu there are two options that say "Minimum" and "Maximum." Both functions will ask for bounds, so pick two points on either side of the vertex that won't overlap with the other one.

Other kinds of calculators probably use a similar routine.

Of course you can always do a binary search, but that takes a lot longer. Let me know if you need help with this.

-Dan