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Lami’s Theorem


If three forces acting at a point on a rigid body are in equilibrium, each force will be proportional to the sine of the angle between the other two forces. Refer Fig. 1.11 (a) & (b)

The mathematical expression of Lami’s theorem is  p/sinα= Q /sin β =S /sin γ

Proof: Applying sine rule for the triangle (Fig. 1.11)  (b)

p/ sin (180°- α)=Q sin (180°- β)= S / sin (180°- r)

p /sin α =Q  sin β =S /sin γ.  Proved.