Răspuns:
1 R=F1+F2 (vectorial)
lRl=l4F1l scalar=>
R²=F1²+F2²+2F1*F2cos 90° cos90°=0
(4F1)²=F1²+F2²+2*F1F2*0
16F1²=F1²+F2²
16F1²-F1²=F2²
15F1²=F2²
F1²/F2²=1/15
F1/F2=√1/15 amplifici cu√15 si obtii
F1/F2=√15/15
2.R²=F1²+FF2²+2F1F2cosα
6²=6²+6²+2*6*6cosα
36=36+36+72cosα
0=36+72cosα
-36=72cosα
cosα=-36/72= -1/2
α=120°
Explicație: