How do you convert x^2+y^2=9x2+y2=9 into polar form?

1 Answer
Dec 29, 2015

Use the substitutions x = rcos(theta)x=rcos(θ) and y = rsin(theta)y=rsin(θ)

Explanation:

Use the substitutions x = rcos(theta)x=rcos(θ) and y = rsin(theta)y=rsin(θ)
Then the equation becomes
r^2cos^2(theta) + r^2sin^2(theta) = 9r2cos2(θ)+r2sin2(θ)=9
r^2(cos^2(theta) + sin^2(theta) ) = 9r2(cos2(θ)+sin2(θ))=9
Because we know that cos^2(theta) + sin^2(theta) = 1cos2(θ)+sin2(θ)=1
this gives r^2 = 9r2=9 and hence r= 3r=3