# Double integral help

1. Aug 10, 2011

### haris13

∫u=3 and l=0 u= x and l= 0∫ (x2 + y2 )dydx

solve by reversing the order of integration. u and l means upper and lower limit. this is a double integral by the way. i dont understand how the limits are found when reversing the order and the idea of diagrams. please help me

2. Aug 10, 2011

### SammyS

Staff Emeritus
I take it you need to do the following integration by reversing the order of integration.

$$\int_0^3\int_0^x\,(x^2+y^2)\,dy\,dx$$

Sketch the region in the xy-plane.

Then consider how you might cover the same region with the order reversed.

3. Aug 10, 2011

### haris13

can you please help me with it. i have been trying to do it since last week. how do u change the limits with the order. thats my question. can you please explain for this particular question?

4. Aug 10, 2011

### Staff: Mentor

To repeat what SammyS said, sketch the region over which integration is being done. The limits of integration are x = 0 to x = 3, and y = 0 to y = x. What does this region in the plane look like?

5. Aug 10, 2011

### haris13

thanks alot..i got it :)