xy面 AH FT FBH X F+ LRH =0 1284.8 R F Bh N=642.4N 2 RAH+F-RBH =0 Rm=-RBm=12848-642.4N=6424Nxy 面 : x y FAH F T FBH 0 2 t BH L − + = F LR1284.8 642.4 2 2 t BH F R N N = = =0 − + − = R F R AH t BH 1284.8 642.4 642.4 R F R N N AH t BH = − = − =