# coordinates of intersection for polar curves

• Apr 25th 2018, 06:58 PM
lc99
coordinates of intersection for polar curves
I have r =2 and r=3+2sintheta

--> 2=3+2sintheta
---> sintheta = -1/2

theta = 4pi/3 , 11pi/6

coordinates (4pi/3,2), (11pi/6,2)

Did i do something wrong?
• Apr 25th 2018, 07:14 PM
topsquark
Re: coordinates of intersection for polar curves
Quote:

Originally Posted by lc99
I have r =2 and r=3+2sintheta

--> 2=3+2sintheta
---> sintheta = -1/2

theta = 4pi/3 , 11pi/6

coordinates (4pi/3,2), (11pi/6,2)

Did i do something wrong?

Actually it should be points in the form $\displaystyle (r, ~ \theta )$, not $\displaystyle ( \theta, ~ r)$.

I'm getting $\displaystyle sin( \theta) = -1/2 \implies \theta = -\frac{\pi}{6} + \pi = \frac{5 \pi}{6} \text{ and } \theta = -\frac{\pi}{6} + 2 \pi = \frac{11 \pi}{6}$

-Dan
• Apr 25th 2018, 07:26 PM
lc99
Re: coordinates of intersection for polar curves
would 5pi/6 give positive value?
• Apr 26th 2018, 11:47 AM
topsquark
Re: coordinates of intersection for polar curves
Quote:

Originally Posted by lc99
would 5pi/6 give positive value?

Whoops! I was thinking of cosine I should have said $\displaystyle \frac{\pi}{6} + \pi = \frac{ 7 \pi}{6}$. The other angle I listed is correct.

Thanks for the catch.

-Dan