Three forces 9 N, 12 N and 15 N acting at a point are in equilibrium the angle between 9 N and 15 N is

We can see that (9)2+(12)2=152 So, forces 9 and 12 are perpendicular to each other. tan⁡α=129=43sin⁡α=4/5 Angle between 9N and 15N is π−α=π−cos−1⁡(3/5)