# Thread: Polar Equation: Draw and Fill in chart

1. ## Polar Equation: Draw and Fill in chart

Draw and fill in the chart that has a row for "Theta" and a row for "r" for this polar equation: r=1-3cos(theta)

I have to fill in the 24 spots (12 for theta and 12 for r) on the chart using this polar equation: r=1-3cos(theta).

2. ## Re: Polar Equation: Draw and Fill in chart

Hve you been introduced to ...polar plot r&#61;1-3cos&#40;t&#41; - Wolfram|Alpha ?

3. ## Re: Polar Equation: Draw and Fill in chart

Thank you very much. How would I go about solving for R when cos(theta)= pi/12?

4. ## Re: Polar Equation: Draw and Fill in chart

Originally Posted by Binary
Thank you very much. How would I go about solving for R when cos(theta)= pi/12?
I think you mean ... "how can I evaluate $\displaystyle r$ when $\displaystyle \theta = \frac{\pi}{12}$" ?

$\displaystyle r = 1 - 3\cos\left(\frac{\pi}{12}\right)$

$\displaystyle r \approx 0.966$

by hand ...

$\displaystyle \cos\left(\frac{\pi}{12}\right) = \cos\left(\frac{\pi}{3} - \frac{\pi}{4}\right)$

... use the difference identity for cosine.

5. ## Re: Polar Equation: Draw and Fill in chart

Originally Posted by skeeter
I think you mean ... "how can I evaluate $\displaystyle r$ when $\displaystyle \theta = \frac{\pi}{12}$" ?

$\displaystyle r = 1 - 3\cos\left(\frac{\pi}{12}\right)$

$\displaystyle r \approx 0.966$

by hand ...

$\displaystyle \cos\left(\frac{\pi}{12}\right) = \cos\left(\frac{\pi}{3} - \frac{\pi}{4}\right)$

... use the difference identity for cosine.
Yeah I figured it out finally then just saw your post. Thank you very much. I was trying to do it by hand btw.

6. ## Re: Polar Equation: Draw and Fill in chart

When I use my calculator I dont get r=0.966. I get approx r=-1.897

7. ## Re: Polar Equation: Draw and Fill in chart

Originally Posted by Binary
When I use my calculator I dont get r=0.966. I get approx r=-1.897
you're correct ... I only punched in $\displaystyle \cos\left(\frac{\pi}{12}\right)$ , my mistake.