You are Here: Home >< Maths

# integral watch

Announcements
1. trying to integrate x^2 + y^2 dx dy over the region bounded by y=x, y=x+2, y=-x, and y=-x+2

so im changing variable using u=x+y v=x-y, but using change of variable i get the answer to be -8/3, whereas computing it straight i get 8/3...not sure what's going wrong? Which is the right answer?

2. The Jacobian is negative - are you taking the modulus of it?
3. ??
4. Err, yes, you do, mandaben / King of TSR.
5. (Original post by King of TSR)
I thought it was just the determinant of the matrix thing rather than the modulus - is that not what the lines mean in this context?

or is the jacobian always positive?
The Jacobian, denoted J, is defined to be a determinant, not a matrix. So |J| means the absolute value of the determinant.
6. haha okay!
7. hijacked
8. http://en.wikipedia.org/wiki/Jacobia...nd_determinant

in the example here the jacobian is negative?
9. ahh i see now..

delete?
10. (Original post by mandaben)
http://en.wikipedia.org/wiki/Jacobia...nd_determinant

in the example here the jacobian is negative?
Yeah, but in the example (under Jacobian determinant) they're merely computing the determinant and not doing actually utilizing it. Whereas the substitution rule specifically requires the absolute value of the determinant.

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: February 5, 2010
Today on TSR

### University open days

1. Norwich University of the Arts
Fri, 28 Sep '18
2. Edge Hill University
Faculty of Health and Social Care Undergraduate
Sat, 29 Sep '18
3. Birmingham City University
Sat, 29 Sep '18
Poll
Useful resources

### Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

### How to use LaTex

Writing equations the easy way

### Study habits of A* students

Top tips from students who have already aced their exams