Lami's theorem relates three nonzero, coplanar force vectors that are not all collinear
and act at a common point in equilibrium. If 
and 
is the angle between the other
two force vectors, then
 |
The result follows from the law of sines applied to the triangle formed by placing the three vectors
successively head to tail. Each interior angle of this
triangle is supplementary to the corresponding 
, and supplementary angles
have equal sines.
