Refer to image for problem.
I have to find the magnitude of the force F3. I'm stuck on where to begin.
The Attempt at a Solution
I've done. cos(y)=sqrt(1-cos^2(60)-cos^2(45))
I got the y angle to be 60. I don't know what that means so if someone could explain that would be great. I just used this because I thought I needed to know that. I then tried to break down each force vector into their components.
F = x, y, z
F1=80(4/5), 0, 80(3/5)
F2=0, 0, -110
FR=120cos(60), 120cos(60), 120cos(45)
Thats all I got. I don't know what to do now.