Equilibrium of body - force acted at any angle:

Magnitude of force 'p' which is required to move the body down the plane. When 'p' is acted with an angle of φ.

Resolving the forces which are Parallel to Plane OA:

PcosΦ  + µR - W.sin α  = 0                                                                                                                ...(i)

Resolving the forces which are Perpendicular to Plane OA:

R + PsinF   - W.cos α  = 0                                                                                                              ...(ii)

Putting value of 'R' from (ii) in equation (i) we get

P = W.[(sin  α  - µ.cosα  )/(cos  Φ- µ.sin Φ )]

Now putting µ = tan θ , on solving

P = W.[sin(α   -Φ )/cos(Φ + θ)]