Bending of Light rays!

If light passes near a massive object, the gravitational interaction causes a bending of the ray. This can be thought of as happening due to a change in the effective refractive index of the medium given by $$\large n(r) = 1 + 2\frac{GM}{rc^2}$$ where $$r$$ is the distance of the point of consideration from the center of the mass of the massive body, $$G$$ is the universal gravitational constant, $$M$$ the mass of the body and $$c$$ the speed of light in vacuum. Considering a spherical object, find the deviation of the ray $$\theta_0$$ from the original path as it grazes the object.

If $$\large \theta_0 = n_1\frac{GM}{rc^{n_2}}$$, find $$n_1 + n_2$$.

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