A ray with angle of incidence 60° is passed through a prism of angle 15°.
To find the net deviation I know we just apply Snell’s law twice for the ray refracting while going in and while coming out. Here’s my doubt - we find $r_1$ (Angle of refraction 1) to be 30°, and $r_2$ can be found out with the help of the relation $$A=r_1+r_2$$ which we get as -15°, what is the significance of the minus sign?
It means that, given the axis you have chosen, there's a 15 degrees inclination in the opposite direction. Negative angles don't have any particular or strange meaning, you could as well say it's +345 degrees.