The point (8,2,9) is in the first octant. The closest distance from the coordinate planes is the value y=2, which will therefore be the maximum radius of the required sphere.
The standard equation of a sphere with radius r and centre (u,v,w) is given by (x-u)^2+(y-v)^2+(z-w)^2=r^2
Substituting r=2, u=8, v=2, w=9, we get the equation of the required sphere (x-8)^2+(y-2)^2+(w-9)^2=2^2
