If curves cut at right angle if 8k² = 1 then vice versa also true. So, we have to prove that 8k² = 1 if curve cut at right angles.

If curve cut at right angle then the slope of tangent at their intersecting point satisfies the relation m₁m₂ = -1

We have to find intersecting point of two curves.

x = y² and xy = k then and