lim h趨向0(x+h)^3—x^3/h(即分母是h,分子是(x+h)^3)求極限請寫下過程,

lim h趨向0(x+h)^3—x^3/h(即分母是h,分子是(x+h)^3)求極限請寫下過程,

lim h趨向0 [(x+h)^3—x^3]/h
=lim h趨向0 [3x^2 *h +3x*h^2 +h^3]/h
=lim h趨向0(3x^2 +3xh +h^2)
=3x^2