Change of variable

[squenshl]

How do I evaluate the triple integral \int\int\int_G x+y+z dV using a suitable change of variable where G is the region
0 \leq x+y \leq 1, 2 \leq y+z \leq 3, 4 \leq x+z \leq 5.
I know to let u = x+y, v = y+z, w = x+z and I end up with the
det(jac) = |2| \Rightarrow 1/det(jac) = |1/2|. But I'm stuck after that. Help.

[tiny-tim]

Hi squenshl! :wink:
How do I evaluate the triple integral \int\int\int_G x+y+z dV using a suitable change of variable where G is the region.

Well, you've got the bounds, and you know how to rewrite the dV (from the Jacobian), so all you need is to rewrite x+y+z in terms of u v and w, which is … ? :smile:

[arildno]

Hint:

What does u+v+w equal, in terms of x+y+z?

[squenshl]

u+v+w = 2x+2y+2z = 2(x+y+z),
\Rightarrow x+y+z = (u+v+w)/2.
Then just chuck that in. Is that right. Thanks.

[tiny-tim]

x+y+z = (u+v+w)/2.

:biggrin: Woohoo! :biggrin:

[squenshl]

Cheers.