Lizcat said:hehe, the question stumped me abit, but then i said.. i;ll get back to it at the end..
you differentiate the y=x^3, and say that 3x^2 has to equal 12.. find x, and sub into the x^3=12x +b, and there u have b!!
Discriminant applies for a quadratic. This is a cubic, so you could have differentiated to get a quadratic, but that's not doing anything for you. The basic principle here is that a tangent exists where gradients are equal. so we know the gradient of y = 12x + b is 12, so where y = x^3 has gradient 12, then given that you can change your b value, the x-coordinates give you the first piece of the puzzle to get b.Bricnic said:I thought this was a question involving the discriminant... don't you have to find values of b which make the discriminant 0, so as to give only one solution (and therefore make 12x +b a tangent)? Could be wrong, but this is how I went about it, not sure what answer I wound up with.