posted by henry baliz .
let f(x)= -x^2 - 1. evaluate f(x)at x=6, -6
So we see that for this particular function, f(6)=f(-6).
In fact, since f(x) is an even function (consisting of even powers of x), this property of f(x)=f(-x) is true for all values of x.
You can try out other pairs, such as f(2) and f(-2) to verify this property.