If f(x)=1-x^2, then f(x-h)=?
We're just substituting (x - h) for x....so we have
1 - (x - h)^2 =
1 - [x^2 - 2xh + h^2 ] =
1 - x^2 + 2xh - h^2 =
-x^2 + 2xh - h^2 + 1
