Official solution
Slope of AB = \[{{ - h} \over k}\]
Equation of AB is hx + ky = h2 + k2
A \[\left( {{{{h^2} + {k^2}} \over h},0} \right),B\left( {0,{{{h^2} + {k^2}} \over k}} \right)\]
AB = 2R
\[ \Rightarrow \] (h2 + k2)3 = 4R2h2k2
\[ \Rightarrow \] (x2 + y2)3 = 4R2x2y2