If you think I'm dishonest, feel free to get the moderators involved. Right, because you apparently don't understand my point, let's plug in some dummy numbers: y = x + 5 k = 1 x > 0 (actually not needed in this case) Then always: y > kx dy/dx = 1 k = 1 dy/dx > k 1 > 1 But 1 is not larger than 1. QED. I have just proved it wrong once again. No, I do not admit that your obviously wrong derivation is correct, obviously. OK, one by one.