Applied Mechanics and Graphic Statics
The centre of gravity of a trapezoidal dam section whose top width is a, bottom width is band the vertical side is a, from its vertical face is

(b² + bc + c²)/3 (b + c)
(a² + ab + b²)/3 (a + b)
None of these
(a² + ab + c²)/3 (a + c)

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Applied Mechanics and Graphic Statics
Lami's theorem states that

Three forces acting at a point are always in equilibrium
Three coplanar forces acting at a point will be in equilibrium if each force is inversely proportional to the sine of the angle between the other two
If three forces acting on a point can be represented in magnitude and direction by the sides of a triangle, the point will be in the state of equilibrium
Three coplanar forces acting at a point will be in equilibrium, if each force is proportional to the sine of the angle between the other two

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