# Homework Help: Polar coordinates finding area between two curves

1. Apr 20, 2008

### th3plan

1. The problem statement, all variables and given/known data

2. Relevant equations

r=sinx
r= cosx

Ok , i need help how to properly select the integral to evaluate the area they make. Can someone please show me how , i know how to evaluate it just having hard times with integrals

3. The attempt at a solution

2. Apr 20, 2008

### EngageEngage

it will be easiest if you first draw out the curves. This will help you figure out what your integral should be.

3. Apr 20, 2008

### th3plan

i graphed it on calculator, and i did set them equal to each other to get tanx=1 but from here on idk what to do

4. Apr 20, 2008

### ice109

first of all over what interval?

5. Apr 20, 2008

### EngageEngage

if you're given those in parametric form in polar, you are going to get two circles in the x,y (or r,theta) plane, i believe. But as ice109 said, its also important that you know how x varies for this one.

6. Apr 20, 2008

### th3plan

the interval is 0,2pi

7. Apr 20, 2008

### rocomath

Multiply both sides by r, then change to rectangular form. Is this Calculus 2 or 3? B/c I did this problem yesterday.

8. Apr 20, 2008

### th3plan

Calc 2

9. Apr 21, 2008

### th3plan

how would i change it to rectangular form, using x=rcos(theta) and y=rsin(theta)

?

10. Apr 21, 2008

### HallsofIvy

No, it isn't. Since sine and cosine are negative for half that interval using 0 to 2$\pi$ gives you each circle twice. And, in fact, the area you want only requires $\theta$ going from 0 to $\pi/2$.

However, you are correct that the circles intersect when tan$\theta$= 1- that is, at $\theta= \pi/4$ as well as at 0. For $0\le \theta\le \pi/4$, a radius goes from 0 to cos($\theta$) while from $\pi/4\le \theta\le \pi/2$ it goes from 0 to sin($\theta$). From symmetry, you should be able to integrate cos($\theta$) from 0 to $\pi/4$ and double.