F→=F1→+F2→+F3→=F1→+F23→
F23→=F2→+F3→
⇒F232=F22+F32+2F2.F3.cos(F2→,F3→)
=6002+8002+2.600.800.cos75o
=1248466,283 (N)
⇒F23=1248466,283=1117,347879 ≈1117,35 (N)
cos(F23→,F3→)=F232+F32−F222.F23.F3=1248466,283+8002−60022.1117,35.800≈0,855
(F23→,F3→)^≈31o => (F23→,F1→)^ = 45o -31o =14o
F→=F1→+F23→
⇒F2=F232+F12+2F23.F1.cos(F23→,F1→)
=1248466,283+15002+2.1117,35.1500.cos14o
=6750946,072
⇒F=6750946,072=2598,258277 ≈2598 (N)