Double integration problem

hora

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Feb 19, 2020
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Hey there, me and my friends have been trying to solve this double integration problem that we have but seems like we can't find a solution, we would love to hear what you might have to help us!

Here is the question:

∫ ∫D ( xy^2)/2048 dxdy , where D is the limited area in the right halfplane that lays inside the circle x^2+y^2=128 and the curve y^2=8x

the problem with this question is which limits we should have for our integrals,

what we think we should have is for x to be [0, sqrt(128)] and y to be either [-8,8] or [8x,sqrt(128-x^2)] but we dont get the right answer when we do this.

I also attached a picture so you can see where the lines intersect so you maybe understand our reason better for why we would think this. My only guess is that we maybe should try polar coordinates instead as this doesnt seem to workaaaaaaaa.PNG
 
1) Why would you do the half plane when you can do the 1st quadrant and multiply by 2? ALWAYS take advantage of symmetry.
2) Solve each equation for x. This will provide your x-limits. Pick the correct piece of the circle. Get them in the right order.
3) No reason why Polar Coordinates wouldn't work. Be careful. No rushing or panicking.
 
With that nice graph it would seem that the symmetry would have jumped right out at you. Please post your work when you are done.
 
With that nice graph it would seem that the symmetry would have jumped right out at you. Please post your work when you are done.
yes the symmetry makes it so that i can simplify the y integral, but i still seem to get the wrong limits, would love if you maybe could help me with that!
 
Please show us your work so we can see where you are making any mistakes. We want you to solve the problem with help from us.
 
Before you receive more help, can you please post the region 0<x<8 and 0<y<sqrt(128) or at least describe it?
I want you to see if that region looks like the region in your diagram.
 
You seem to have overlooked point #2; repeated here:

2) Solve each equation for x. This will provide your x-limits. Pick the correct piece of the circle. Get them in the right order.

4) Please answer Jomo's question. What region is this? 0<x<8 and 0<y<sqrt(128). Is it the right sort of region?
 
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