100 ③3、4(1,2) P 2(0,0) P 0 ∫100「2268576o 3m 576243202 4.69 1(0,0) 3(0,0) 4m F 20 20‖01000 22.2 2020‖000114.69 22.2 图19 37.03 43‖469 37.03 M1=-222(压力) 15-15 7035N2=3703拉力) 151500104697035N3=70.35(拉力)P 4m 3m 3 1 2 1(0,0) 2(0,0) 3(0,0) 4(1,2)         = 0 100 P             =       2 1 5.76 24.32 22.68 5.76 0 100         − =       1.11 4.69 2 1         − =               −             − − =       22.2 22.2 1.11 4.69 0 0 0 0 0 1 0 1 0 0 20 20 20 20 1 2 1 F F      − =               −                 − − =       37.03 37.03 1.11 4.69 0 0 5 3 5 4 0 0 0 0 5 3 5 4 12 12 12 12 2 2 1 F F      − =               −             − − =       70.35 70.35 1.11 4.69 0 0 0 0 1 0 1 0 0 0 15 15 15 15 3 2 1 F F N1 = −22.2 (压力) N2 = 37.03 (拉力) N3 = 70.35 (拉力)