The distance between the parallel planes ax + by + cz + d1 = 0 and ax + by + cz + d2 = 0 is d=|d1−d2| / (√a2+b2+c2). find equations of the planes that are parallel to the plane x + 2y − 2z = −1 and three units away from it. (enter your answers as a comma-separated list of equations.)