F122=F12+F22+2.F1.F2.cos\(\alpha\)
F122=202+102+2.20.10.cos(90)=500(N)
=>F12=10\(\sqrt{5}\)(N)
F232=F22+F32+2.F2.F3.cos\(\alpha\)
F232=102+102+2.10.10.cos30=373,2(N)
=>F23=19,32(N)
F132=F12+F32+2F1.F2.cos\(\alpha\)
F132=202+102+2.20.10.cos240=300(N)
=>F13=10\(\sqrt{3}\)(N)
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