if f(x) = x2 + 2x, then find f(a+h)-f(a)
subsitute a+h for x and a for xf(a+h)-f(a)=(a+h)^2+2(a+h)-(a^2+2a)a^2+2ah+h^2+2a+2h-a^2-2a2ah+h^2 is the result
