How do you convert r^2 = 9cos5(theta)r2=9cos5(θ) into cartesian form?

1 Answer

1/9 (x^2+y^2)^3.5-x^5+10x^3y^2-5xy^4=019(x2+y2)3.5x5+10x3y25xy4=0. Graph is inserted

Explanation:

Here, 9 cos 5theta = r^2 >=09cos5θ=r20. So, 5theta5θ is in Q1 or Q4.

And so, thetaθ is in 2kpi+-(1/5)pi/22kπ±(15)π2, k = 0, 1, 2, 3...

The period for the graph is (2pi)/5=72^o2π5=72o.

For one half (36^o36o) r^2r2 is positive. For the other, r^2< 0r2<0.

Only for half period = pi/5 = 36^oπ5=36o, the graph appears.

I expect five equal loops like the ones that are marked red in the

second graph, contributed by the other author.

The conversion formula is r(cos theta, sin theta)=(x, y)r(cosθ,sinθ)=(x,y), with

r=sqrt(x^2+y^2)>=0r=x2+y20.

Substitution gives the form in the answer.

graph{(x^2+y^2)^3.5-9x^5+90x^3y^2-45xy^4=0}

Debugging was elusive for me, for so long. I was able to do it now.

Adikesavan's revised answer ends here.

Here is a graph where the red is the positive value for r and the green is the negative values for r:
![Desmos.com](useruploads.socratic.orguseruploads.socratic.org)