How Do You Estimate a Double Integral Using Riemann Sums?

AATroop
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Homework Statement


If R = [0,4]x[-1,2], use a Riemann sum with m=2, n=3 to estimate the value of ∫∫(1-xy^2)dA. Take the sample points to be the lower right corners.

Homework Equations


None

The Attempt at a Solution


2*1[f(2,-1) + f(2,0) + f(2,1) + f(4,-1) + f(4,0) + f(4,1)] = some value

Just wondering if the setup is correct, particularly the 2 and the 1 at the beginning.

Edit:

Would the solution for the upper left corners of the rectangles be

2*1[f(0,-1)+ f(0,0)+ f(0,1) +f(2,-1) + f(2,0) + f(2,1)]
 
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AATroop said:

Homework Statement


If R = [0,4]x[-1,2], use a Riemann sum with m=2, n=3 to estimate the value of ∫∫(1-xy^2)dA. Take the sample points to be the lower right corners.


Homework Equations


None


The Attempt at a Solution


2*1[f(2,-1) + f(2,0) + f(2,1) + f(4,-1) + f(4,0) + f(4,1)] = some value

Just wondering if the setup is correct, particularly the 2 and the 1 at the beginning.

Yes, that looks OK

Edit:

Would the solution for the upper left corners of the rectangles be

2*1[f(0,-1)+ f(0,0)+ f(0,1) +f(2,-1) + f(2,0) + f(2,1)]

(0,-1) isn't the upper left corner of any rectangle. Did you accidentally do lower left?
 
Yes, I think I did do lower left. I changed it and it came out to -8. Sounds close enough to me haha. Thanks a bunch for your help.
 
There are two things I don't understand about this problem. First, when finding the nth root of a number, there should in theory be n solutions. However, the formula produces n+1 roots. Here is how. The first root is simply ##\left(r\right)^{\left(\frac{1}{n}\right)}##. Then you multiply this first root by n additional expressions given by the formula, as you go through k=0,1,...n-1. So you end up with n+1 roots, which cannot be correct. Let me illustrate what I mean. For this...

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