lim h menuju 0 f(x+h)-f(x)/h jika f(x)=3x kuadrat +5x+7

((3(x+h)^2 +5(x+h)+7) - (3x^2 +5x +7))/h
= ((3x^2 +6xh +3h^2 +5x+5h+7) - 3x^2 -5x-7))/h
= (3h^2 +6xh +5h)/h
= 3h + 6x + h

limit 3h +6x +h = 6x
h->0