Evaluate if possible the function at the given value of the independent valuable.

f(x)=x^3

f(x+delta x-f(x)/(delta x)

This is what I did

f(x+delta x)^3-f(x)

I got

(x^2+2(delta)x+delta(x)^2) (x+delta(x))-f(x)

Which then I put into

x^3 + 2 delta(x) * x + delta(x)^2 * x + x^2*delta(x)+2delta(x)delta(x)+delta(x)^3

Which I simplified

x^3 + 2x*delta(x) + x*delta(x)^2 +x^2*delta(x) + 2delta(x)^2 + delta(x)^3-f(x)/(delta x)

But I am stuck any help would be appreciated