Change of Variables: Evaluating Double Integral over R with Cosine Function

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SUMMARY

The discussion focuses on evaluating the double integral of the cosine function, specifically cos[(y-x)/(y+x)], over a trapezoidal region defined by the vertices (1,0), (2,0), (0,1), and (0,2). The transformation to the uv-plane is initiated using the substitutions u=y-x and v=y+x. The limits for v are established as v=1 and v=2, while the limits for u are derived from the equations u+v=2y and u-v=-2x, leading to the conditions u=v and u=-v. The challenge lies in determining the appropriate limits for u in this transformation.

PREREQUISITES
  • Understanding of double integrals and their evaluation
  • Familiarity with coordinate transformations in multivariable calculus
  • Knowledge of the cosine function and its properties
  • Ability to interpret trapezoidal regions in the Cartesian plane
NEXT STEPS
  • Study the method of change of variables in double integrals
  • Learn how to derive limits of integration for transformed variables
  • Explore examples of evaluating integrals over non-rectangular regions
  • Investigate the properties of the cosine function in integral calculus
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Students and educators in calculus, particularly those focused on multivariable calculus and integral evaluation techniques, as well as anyone seeking to deepen their understanding of coordinate transformations in mathematical analysis.

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Homework Statement


Evaluate the double integral over R of cos[(y-x)/(y+x)] dA where R is the trapezoidal region with vertices (1,0) (2,0) (0,1) and (0,2).


The Attempt at a Solution



First I set u=y-x, v=y+x. I have 4 sides in the xy-plane that need to be transformed into the uv-plane. Side 1 is y=-x+2, Side 2 is y=-x+1, and then Side 3 & 4 are 0<x<2 (where the less than sign signifies less than or equal to).

I solved for v, and got v=1, v=2, so I have those limits. But I can't figure out how to find the limits for u.
 
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u+v = 2y
u-v = -2x

using x = 0, y =y and x =x, y = 0

you can get u = v and u = -v

I don't know better method to find these limits
 

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