How to eliminate $\theta$? While doing a sum I was stuck in a particular step:
$$r_1= \frac{4a \cos \theta }{\sin^2 \theta}$$ and $$r_2=\frac{4a \sin \theta }{\cos^2 \theta}$$
How to eliminate $\theta$ ?

we get $$\sin(x)^2=\frac{4a\cos(x)}{r_1}$$ and $$\cos(x)^2=\frac{4a\sin(x)}{r_2}$$ adding both we obtain
$$1=\frac{4a\cos(x)}{r_1}+\frac{4a\sin(x)}{r_2}$$
now you can write
$$1-\frac{4a\cos(x)}{r_1}=\frac{4a\sin(x)}{r_2}$$ and square it.
