The direction of three forces acting on a line has to be concurrent?

[Jason Ko]

TL;DR

I found this theorem in D. Morin's book on mechanics. How to prove it mathematically? Does it have a name?

 

[Orodruin]

Take the point of crossing of two of the force lines of action. If the third line of action does not pass through that crossing, there is a net torque and therefore this cannot happen for a system in equilibrium.

 

[Jason Ko]

Thanks! I was being stupid

 

[kuruman]

Thanks! I was being stupid

Probably you didn't read the "simple" proof provided below the statement that you highlighted in the textbook.

 

[Orodruin]

Probably you didn't read the "simple" proof provided below the statement that you highlighted in the textbook.

Nor I. Good thing I agree with Morin though …