Intersection of 2 curves at right angles

Hey guys, I have a question that I am stuck atm and need some help with.

**"For what values of the nonzero constant k do the curves y=kx^2 and y=k(x-2)^2 intersect at right angles?"**

I started off by finding the intersection point of the 2 curves:

kx^2 = k(x-2)^2

x = 2

After which I differentiate to find my gradient or slope:

For the curve y = kx^2, **m1** = 2kx

For the curve y = k(x-2)^2, **m2** = 2k(x-2)

I understand that since the 2 curves intersect at 90 degrees, m1.m2 = -1

But when i sub x=2 into my m2, i get 0 which gives me m1.0 = -1

I am definitely wrong somewhere but I cannot really figure it out. Am I even on the right track to solving this question?

Cheers,

Dickson