用余弦定理
F1=sqrt(2×100^2-2×100×100×cos(180-90))=141N
F2=sqrt(2×100^2-2×100×100×cos(180-60))=173N
F3=sqrt(2×100^2-2×100×100×cos(180-120))=100N
用余弦定理
F1=sqrt(2×100^2-2×100×100×cos(180-90))=141N
F2=sqrt(2×100^2-2×100×100×cos(180-60))=173N
F3=sqrt(2×100^2-2×100×100×cos(180-120))=100N