A point `P` moves on a plane `x/a+y/b+z/c=1.` A plane through `P` and perpendicular to `O P` meets the coordinate axes at `A , Ba n d Cdot` If the planes through `A ,Ba n dC` parallel to the planes `x=0,y=0a n dz=0,` respectively, intersect at `Q ,` find the locus of `Qdot`