# Find all points of intersection

• Jul 19th 2011, 04:30 PM
centenial
Find all points of intersection
I'm asked to find all points of intersection between

$r=1-\cos{\theta}$ and
$r=1+\sin{\theta}$.

I've graphed both polar equations. The first one looks like a heart rotated 90 degrees to the right. The second like a heart flipped vertically.

I know that I'm supposed to set the equations equal to each other:

$1-\cos{\theta} = 1+\sin{\theta}$

$\cos{\theta} + \sin{\theta} = 0$

So, I need something that either makes both cos and sin zero, or makes them opposites of each other.

So, $\theta = \frac{3\pi}{4}$. But now that I have that, I'm not really sure how to proceed. Do I integrate one of the functions from 0 to $\frac{3\pi}{4}$?

Confused...
• Jul 19th 2011, 05:20 PM
pickslides
Re: Find all points of intersection
Quote:

Originally Posted by centenial

$\cos{\theta} + \sin{\theta} = 0$

So, I need something that either makes both cos and sin zero, or makes them opposites of each other.

$\cos{\theta} + \sin{\theta} = 0$

$-\cos{\theta} = \sin{\theta}$

$-1 = \frac{\sin{\theta}}{\cos{\theta}}$

$-1 = \tan{\theta}$

Solve this? Then sub in for $r$
• Jul 20th 2011, 03:19 AM
mr fantastic
Re: Find all points of intersection
Quote:

Originally Posted by centenial
I'm asked to find all points of intersection between

$r=1-\cos{\theta}$ and
$r=1+\sin{\theta}$.

I've graphed both polar equations. The first one looks like a heart rotated 90 degrees to the right. The second like a heart flipped vertically.

I know that I'm supposed to set the equations equal to each other:

$1-\cos{\theta} = 1+\sin{\theta}$

$\cos{\theta} + \sin{\theta} = 0$

So, I need something that either makes both cos and sin zero, or makes them opposites of each other.

So, $\theta = \frac{3\pi}{4}$. But now that I have that, I'm not really sure how to proceed. Do I integrate one of the functions from 0 to $\frac{3\pi}{4}$?

Confused...

What has integration got to do with the question as posted.