120 65 (a) F ZE=0, FAr +FccosacosB=0 ∑F,=0,F+F2+F B=0 ∑ FAc+ P- Resina- FB=o 根据题5-3图(b)所示几何关系,可得 a=26.57°,B=22.62 解①式,得 F 25P 25×260 kN=291 kN 解②式,得