# Line integral Problem

1. Apr 5, 2010

### joemabloe

1. The problem statement, all variables and given/known data
Compute the line integral of $$\int$$c ydx +zdy + xdz

where c is the intersection of x^2 +y^2+z^2= 2(x+y) and x+y=2

(in the direction clockwise as viewed from the origin)

2. Relevant equations

3. The attempt at a solution

While attempting this problem I had a few ideas on how to do it but i couldn't figure out how to make any of them work. One Idea I tried was converting to spherical coordinate which gave me:
x= 2sin$$\Phi$$cos$$\Theta$$
y= 2sin$$\Phi$$sin$$\Theta$$
z= 2cos$$\Theta$$
because the intersection of the curves is a sphere with the equation x^2+y^2+z^2=4.

I have a problem here because when I tried to set up an integral for the line derivative, there are two variables but you can only set the integral for one of them.

Am I at least on the right path here?

2. Apr 5, 2010

### vela

Staff Emeritus
That intersection is not correct. The first equation is that of a sphere; the second is that of a plane. So if they intersect at more than one point, the intersection will be a circle.

3. Apr 5, 2010

### lanedance

I think you should find $\theta$ & $\phi$ will be dependent due to the constraints though they may not be simple to solve for

other ideas - an intersection of a plane & a sphere is a circle, so you could try and find the equation of the circle, and parameterise in terms of a single variable

or you could try some variable subsititions, though transforming the line integral would be complicated, so the circle probably seems like the best idea

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