## meww 2 years ago Convert the rectangular equation to a polar equation. y^2-x^2=7sqrt(x^2+y^2)

1. tkhunny

$$x = r\cos(\theta)$$ $$y = r\sin(\theta)$$ Substitute and Simplify.

2. meww

i know that.. but what i got was -rcos(2theta) = 7r and it says the answer is r=-7/cos(2theta)

3. tkhunny

Why didn't you say so? If you show your work, we can have a much better conversation much more quickly. $$x^{2} = r^{2}\cos^{2}(\theta)$$ $$y^{2} = r^{2}\sin^{2}(\theta)$$ $$\sqrt{x^{2} + y^{2}} = r$$ And we're left with: $$r(\sin^{2}(x) - cos^{2}(x)) = 7$$ Sure enough, exctly as you have it. So, what's the dilemma? Not the form allowed by the exam? Try cos(x) = 1/sec(x)