SOLUTION: Write polar equation in rectangular form. r=6sin(theta)

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Question 1036835: Write polar equation in rectangular form.
r=6sin(theta)

Answer by Edwin McCravy(20059) About Me  (Show Source):
You can put this solution on YOUR website!


r%22%22=%22%226sin%28theta%29

If we draw the graph of that on polar graph paper. we make
a table of points:

  q | r
  0院0.00
 15院1.55
 30院3.00
 45院4.24
 60院5.20
 75院5.80
 90院6.00
105院5.80
120院5.20
135院4.24
150院3.00
165院1.55
180院0.00

We get this circle:



When changing from one form to the other always draw this first:



We substitute for the sine first.
Looking at the triangle and remembering that
SINE=OPPOSITE%2FHYPOTENUSE 

sin%28theta%29=y%2Fr

so substitute y%2Fr for sin%28theta%29 first

r%22%22=%22%226%28y%2Fr%29

r%22%22=%22%22%286y%29%2Fr

Multiply both sides by r

r%5E2%22%22=%22%226y

Now use the Pythagorean theorem to substitute x%5E2%2By%5E2
for r%5E2

x%5E2%2By%5E2%22%22=%22%226y  <-- answer

As a check let's graph it.

Get it in standard form:

x%5E2%2By%5E2-6y%22%22=%22%220

Write x as (x-0)

Complethe square:
take half or -6, get -3
Square it, get 9
Add 9 to both sides:

%28x-0%29%5E2%2By%5E2-6y%2B9%22%22=%22%229

Factor the trinomial in y:

%28x-0%29%5E2%2B%28y-3%29%5E2%22%22=%22%229

That's a circle with center (0,3) and radius 3:



It graphs as the same circle, so we are right.

Edwin