P MABc的受力: ●P、AS+PAS+PAS+PAS=0 P=-P dvAz=AS=ASn Pn=Pin+Pin, +Pin2 AzAx=4S.=4Sn Andy=4S. =4Sn x Prrtn y yx ny nP+ Pnz=n, P+nyP +n,p EXIT8 EXIT MABC的受力： P−x ΔSx + P− y ΔSy + P−z ΔSz + Pn ΔS = 0     P n Pn   − = − z z y y x x ΔxΔy ΔS ΔSn ΔzΔx ΔS ΔSn ΔyΔz ΔS ΔSn = = = = = = 2 1 2 1 2 1 Pn Px nx Py ny Pz nz     = + + Pn  Pnx Pny Pnz Px  Pxx Pxy Pxz Py  Pyx Pyy Pyz Pz  Pzx Pzy Pzz = nx = nx = nx + ny + ny + ny + nz + nz + nz