I'm guessing as to what you mean...
You mean symmetry with respect to the y-axis or symmetry with respect to the origin?
If that's the case, then take the original function, plug in (-x) for x. If you get the exact same function, then it's symmetrical with respect to the y-axis. (an "even funtion")
If upon reducing the function, you end up with - (f(x)) Then, it's an odd function, and symmetrical with respect to the origin.