I assume you're new to the Difference Quotient.
Don't let the Difference Quotient scare you.Find . for .
. . Break it down into its three basic steps.
(1) Find . . . Replace with ... and simplify.
(2) Subtract . . . Subtract the original function ... and simplify.
(3) Divide by . . . Factor and cancel (carefully!)
Here we go! . . . We have: .