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### Section 9.6 : Polar Coordinates

8. Convert the following equation into an equation in terms of Cartesian coordinates.

$\frac{2}{r} = \sin \theta - \sec \theta$ Show Solution

There is a variety of ways to work this problem. One way is to first do the following rearranging/rewriting of the equation.

$\frac{2}{r} = \sin \theta - \frac{1}{{\cos \theta }}\hspace{0.5in} \to \hspace{0.5in}\frac{{2\cos \theta }}{r} = \sin \theta \cos \theta - 1$

At this point we can multiply everything by $${r^2}$$ and do a little rearranging as follows,

$2r\cos \theta = {r^2}\sin \theta \cos \theta - {r^2}\hspace{0.5in} \to \hspace{0.5in} 2r\cos \theta = \left( {r\sin \theta } \right)\left( {r\cos \theta } \right) - {r^2}$

We can now use the following formulas to finish this problem.

$x = r\cos \theta \hspace{0.25in}\hspace{0.25in}y = r\sin \theta \hspace{0.25in}\hspace{0.25in}{r^2} = {x^2} + {y^2}$

Here is the answer for this problem,

$\require{bbox} \bbox[2pt,border:1px solid black]{{2x = yx - \left( {{x^2} + {y^2}} \right)}}$