Hi. I can't get what I'm doing wrong here. If somebody points that out, I'm really gratefull. [tex]u = (6 + 2x^2)^3[/tex] [tex]d(u) = 3(6+2x^2)^2 d(6+2x^2)=3(6+2x^2)^2 d(6) + d(2x^2) = [3(6+2x^2)^2 * 0 + 4x]dx = 4xdx[/tex] Then I want to draw a tangent on the point, which acctually lies on the line(!), (1, 512) to check the derivative. [tex]l(x)=f'(a)(x-a)+b=4(x-1)+512=4x+508[/tex] Which don't intersect the curve at (1, 512)... Please correct every misstake I've made. Yes, they could be many; I'm not so good on this stuff.