Applied Mechanics and Graphic Statics
The necessary condition of equilibrium of a body is:

Algebraic sum of the moments of the forces about a point must be zero
All (A), (B) and (C)
Algebraic sum of vertical components of all the forces must be zero
Algebraic sum of horizontal components of all the forces must be zero

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Applied Mechanics and Graphic Statics
Varingon’s theorem of moment’s states

Algebraic sum of the moments of two forces about any point, is equal to the moment of their resultant about that point
Arithmetical sum of the moments of two forces about any point, is equal to the moments of their resultant about that point
Arithmetical sum of the moments of the forces about any point in their plane, is equal to the moment of their resultant about that point
Algebraic sum of the moments of the forces about any point in their plane, is equal to the moment of their resultant about that point

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Applied Mechanics and Graphic Statics
The following is in unstable equilibrium

A satellite encircling the earth
A uniform solid cone resting on its base on a horizontal plane
A solid cube resting on one edge
A uniform solid cone resting on a generator on a smooth horizontal plane

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