MP 1,0, CoSaL. MR=yo o-1 cosB cosy cosr k MPXMR=xoVo1-1 cosa cos a COS B x030 coSr cosy cosr COS 0-1 cos r 所以,截面面积为 A=×M= cos a cOS B cosr cosr COS0 0 cos cos 1, 0, , 0, 1, co s c o s MP x MR y α β γ γ ⎛ ⎞ ⎛ ⎞ = − = − ⎜ ⎟ ⎜ ⎟ ⎝ ⎠ ⎝ ⎠ JJJG JJJG 0 0 0 0 co s c o s co s 1 0 , ,1 co s c o s co s cos 0 1 co s i j k MP MR x y x y α α β γ γ γ β γ ⎛ ⎞ × = − = ⎜ ⎟ ⎝ ⎠ − G G G JJJG JJJG 所以，截面面积为 0 0 cos cos 1 , , 1 . cos cos cos A MP MR x y α β σ γ γ γ ⎛ ⎞ = × = = ⎜ ⎟ ⎝ ⎠ JJJG JJJG