# Thread: Write Using Rectangular Coordinates

1. ## Write Using Rectangular Coordinates

The letters r and theta represent polar coordinates. Write each equation using rectangular coordinates (x,y).

(1) y = 4

(2) r = [3]/[3 - cos(theta)]

2. Originally Posted by magentarita
The letters r and theta represent polar coordinates. Write each equation using rectangular coordinates (x,y).

(1) y = 4

(2) r = [3]/[3 - cos(theta)]
(1) is already expressed in rectangular coordinates.

(2) $\Rightarrow 3r - r \cos \theta = 3$.

Substitute $x = r \cos \theta$ and $r = \sqrt{x^2 + y^2}$.

3. ## sorry

Originally Posted by mr fantastic
(1) is already expressed in rectangular coordinates.

(2) $\Rightarrow 3r - r \cos \theta = 3$.

Substitute $x = r \cos \theta$ and $r = \sqrt{x^2 + y^2}$.
Sorry, the first question should be r = 4 not y = 4.

Can you show me now?

4. ## Also...

The letters r and theta represent polar coordinates. Write each equation using rectangular coordinates (x,y).

The second question is a fraction.

(2) r = [3] divided by [3 - cos(theta)]

5. Originally Posted by magentarita
The letters r and theta represent polar coordinates. Write each equation using rectangular coordinates (x,y).

The second question is a fraction.

(2) r = [3] divided by [3 - cos(theta)]
I realise that. The symbol => means 'it follows that'. Do you see how what I posted follows from the second question.

6. Originally Posted by magentarita
Sorry, the first question should be r = 4 not y = 4.

Can you show me now?
r = 4 => r^2 = 16. Make the obvious substitution.

7. ## I don't....

Originally Posted by mr fantastic
r = 4 => r^2 = 16. Make the obvious substitution.
I don't see the obvious substitution.

8. You should recall that $r^2 = x^2 + y^2$ which should remind you of a circle

9. ## ok

Originally Posted by o_O
You should recall that $r^2 = x^2 + y^2$ which should remind you of a circle
Our teacher did not teach this to the class.