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 = −2 and two units away from it. (enter your answers as a comma-separated list of equations.)