If the function f is defined by f(x)=x^2-2x, find limit h->0
(f(3+h)-(f(3-h))/2h
Do exactly what is suggested, and simplify the resulting expression:
(f(3+h)-(f(3-h))/2h
=((3+h)²-2(3+h)-((3-h)²-2(3-h)))/2h
=...
Take the limit h->0 if necessary.