 #1
 29
 3
 Homework Statement:

A thin stiff uniform rectangular plate with width L (L =AB) is lying on two inclined surface as shown in Fig. 31. The angle between the horizontal surface and the left inclined surface is α, and that between the horizontal surface and the right inclined surface is β. It is assumed that the plate length is sufficiently larger than L and both edges of the plate are smooth enough to neglect friction.
(1) In case of α+β = 90°, the static balance shown in Fig.31 is
 Relevant Equations:

if three forces act on a body in equilibrium,
The sum of vectors is zero
The Vectors cross or intersect at same point and they are in the same plane.
I HAVE NO IDEA HOW TO START.ONLY THINGS I KNOW ARE WHAT I RERAD ON THIS THRED.
https://www.physicsforums.com/threads/equilibriumofastiffplateoninclinedplanes.947601/
I cant continue from there. There are also questions where α=β, α+β=45 and where α=45,β=60.How to make use of the fact that G will follow the arc of a circle centered at O, and that at equilibrium it is vertically above O.