Given the sphere $x^2+y^2+z^2=ax, x^2+y^2+z^2=bx.$ How to prove that the given sphere is reciprocically normal.
My attemp is:
I find: $f_x(x,y,z)=2x-a,f_y(x,y,z)=2y,f_z(x,y,z)=2z$
$f_x(x,y,z)=2x-b,f_y(x,y,z)=2y,f_z(x,y,z)=2z$
but i dint know how to continue