Two forces 5 and 10 kg wt are acting with an inclination of 120 degrees between them. What is the angle which the resultant makes with 10 kg wt?

From the diagram, we can directly find the angle α made by the resultant with the 10 kg wt.

tan α = 5(sin 120)/[10 + 5(cos 120)]

=> tan α = 0.577

=> α = tan^-1(0.577) = 30^o

This is the angle made by the resultant with the 10 kg wt force.