An equation of a plane parallel to the plane x-2y+2z--5=0 and at a unit distance from the origin is
x-2y+2z-7=0
x-2y+2z+5=0
x-2y+2z-3=0
x-2y+2z+1=0
The required plane is x-2y+2z+k=0. The distance to the plane from origin = 1
⇒|k|1+4+4=1⇒k=±3