如图,作MG‖DA∵DA‖CB ∴MG‖CB,
∵AN=DM,AE=DB=√2AB.
∴AN/AE=DM/DB=AG/GB,∴NG‖RB
∵MG‖CB, NG‖RB
∴平面GMN‖平面EBC.
∵MN∈平面GMN
∴MN‖平面EBC..