Optimizing Limits of Integration for Change of Variables

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SUMMARY

This discussion focuses on optimizing limits of integration for a change of variables in a double integral scenario involving a rectangular domain in the first quadrant. The transformation used is defined by the equations x = u + √(u² - v²) and y = u - √(u² - v²), with the condition that v ≤ u. The participant outlines three distinct double integrals with specific limits: DI#1: (a+c)/2 ≤ u ≤ √(bd) and (a+c)/2 ≤ v ≤ u; DI#2: (a+c)/2 ≤ u ≤ (b+d)/2 and √(ac) ≤ v ≤ (a+c)/2; DI#3: √(bd) ≤ u ≤ (b+d)/2 and (a+c)/2 ≤ v ≤ √(bd).

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  • Understanding of double integrals in calculus
  • Familiarity with change of variables in integration
  • Knowledge of the properties of square roots and inequalities
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Students and professionals in mathematics, particularly those studying calculus, as well as researchers and educators looking to deepen their understanding of integration techniques and variable transformations.

eyesontheball1
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Hi guys, I've been on quite a random change of variables binge lately and I've been messing around with a particular scenario in which I'm not 100% sure of how I should choose my limits of integration. Any help would be greatly appreciated! (And no, this is not homework, etc.) The scenario is as follows:

Domain of integration in the xy plane is some rectangle in the 1st quadrant with vertices (a,c), (b,c), (a,d), (b,d), and I want to make a change of variables using x = u + \sqrt{u^2 - v^2} and y = u - \sqrt{u^2 - v^2}. Other than the fact that this transformation would inherently require v≤u, I'm just not certain on how to determine the other numerical limits of integration for u and v.
 
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Update: I think I may have the bounds correct now. If not, someone please correct me. To make this change of variables, you have to express the new integration problem as three separate double integrals, with each of the double integrals having the following general limits of integration:

DI#1: \frac{a+c}{2}≤u≤\sqrt{bd} ; \frac{a+c}{2}≤v≤u

DI#2: \frac{a+c}{2}≤u≤\frac{b+d}{2} ; \sqrt{ac}≤v≤\frac{a+c}{2}

DI#3: \sqrt{bd}≤u≤\frac{b+d}{2} ; \frac{a+c}{2}≤v≤\sqrt{bd}
 

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