How do you convert y^2 =9xy2=9x to polar form?

1 Answer
Apr 1, 2018

r=9cotthetacscthetar=9cotθcscθ

Explanation:

The conversion from Rectangular to Polar:
x=rcosthetax=rcosθ
y=rsinthetay=rsinθ

Substitute for xx and yy:
(rsintheta)^2=9(rcostheta)(rsinθ)2=9(rcosθ)
r^2sin^2theta=9rcosthetar2sin2θ=9rcosθ
r^2sin^2theta-9rcostheta=0r2sin2θ9rcosθ=0
r(rsin^2theta-9costheta)=0r(rsin2θ9cosθ)=0

At this point either r=0r=0 or rsin^2theta-9costheta=0rsin2θ9cosθ=0, let's solve the second one to get a meaningful answer:

rsin^2theta=9costhetarsin2θ=9cosθ

r=(9costheta)/sin^2thetar=9cosθsin2θ

r= (9costheta)/sintheta*1/sinthetar=9cosθsinθ1sinθ

Remember: costheta/sintheta=cotthetacosθsinθ=cotθ and 1/sintheta= csctheta1sinθ=cscθ:

r=9cotthetacscthetar=9cotθcscθ