Line Integral does not match Greens Theorem?

Join the discussion
Registration is free. Ask a follow-up in this thread, or start your own.
2 replies · 2K views
PhantomPower
Messages
14
Reaction score
0

Homework Statement



To evaluate the following line integral where the curve C is given by the boundary of the square 0 < x < 2 and 0 < y < 2 (In the anti clockwise sense):

[itex]\oint (x+y)^2 dx + (x-y)^2 dy[/itex]

The Attempt at a Solution



Firstly it is noted that for a square ABDE :
Between AB, dy = 0 ,y = 0
Between BD, dx = 0 ,x = 2
Between DE, dy = 0 ,y = 2
Between EA, dx = 0 ,x =0

Thus : [itex]\int^2_0 x^2 dx + \int^2_0 (2-y)^2 dy + \int^0_2 (x+2)^2 dx + \int^0_2 -y^2 dy[/itex]
Giving [itex]\frac{x^3}{3} |^2_0 + \frac{-(2-y)^3}{3} |^2_0 + \frac{(x+2)^3}{3} |^0_2 + \frac{-y^3}{3} |^0_2[/itex]

Evaluating gives 10.6? but applying greens theorem gives -16. Can anyone spot my mistake - Probaly a negative sign?

Thanks very much.
P.s sorry for typos this keyboard is broken
 
Physics news on Phys.org
Hi PhantomPower! :smile:

erm :redface:

∫ (2 - y)2 is the same as ∫ (y - 2)2 ! :wink:

(similary for (-y)2)
 
Ooops.

Thanks very much - been a long day...