Since there are two forces acting on the body, So we use Law of Parallelogram of forces.
Case-1: P =20 KN, Q = 15KN, α = 60°
R2 = P2 + Q2 + 2PQ cosα = 202 + 152 + 2 × 20 × 15 cos 60°
R = 30.41KN
tanθ = Q sinα/(P + Q cosα) = 15 sin 60°/(20 + 15 cos 60°)
θ = 25.28º
Case-2: Now angle between two forces is 120º, P = 20KN, Q = 15KN, α =120°
R2 = P2 + Q2 + 2PQ cosα = 202 + 152 + 2 × 20 × 15 cos 120°
R = 18.027KN
tanθ = Q sinα/(P + Q cosα) = 15 sin 120°/(20 + 15 cos 120°)
θ = –46.1º.