Question

平面上三个力F1，F2，F3作用于一点且处于平衡状态，F1的模为1，F2的模为2，F1与F2的夹角为45度，求F3？

F3与F1的夹角为多少？

Answer 1

F3²=F1²+F2²-2*F1*F2*cos(180-45)
=1+4-4cos135°
=5+2√2
F3=√(5+2√2) =2.797933

Answer 2

|F3|=√[|F1|^2+|F2|^2-2|F1||F2|cos135度]
=√1+4+4*√2/2
=√(5+2√2)

Answer 3

1.47