The equation of sphere concentric with the sphere x2+y2+z2−4x−6y−8z−5=0 is x2+y2+z2−4x−6y−8z+c=0...(i) Since, this sphere eq.(i) passes through origin, therefore 0+0+0−0−0−0+c=0 ⇒ c = 0 Hence, the required equation of sphere is x2+y2+z2−4x−6y−8z=0