Solving Change of Variables Homework: Ellipse 9x^2+4y^2=1

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SUMMARY

The discussion focuses on solving a double integral involving the function sin(9x^2 + 4y^2) over the region R bounded by the ellipse defined by the equation 9x^2 + 4y^2 = 1. The participants suggest using the substitutions u = 3x and v = 2y, followed by a transition to polar coordinates in the new variables. This approach simplifies the evaluation of the integral, leading to a clearer path to the solution.

PREREQUISITES
  • Understanding of double integrals and their applications.
  • Familiarity with polar coordinates and transformations.
  • Knowledge of the properties of ellipses in Cartesian coordinates.
  • Experience with trigonometric functions and their integrals.
NEXT STEPS
  • Explore the method of change of variables in double integrals.
  • Learn about polar coordinates and their application in multivariable calculus.
  • Study the properties and equations of ellipses in detail.
  • Practice evaluating integrals involving trigonometric functions.
USEFUL FOR

Students studying multivariable calculus, particularly those tackling double integrals and transformations, as well as educators seeking to enhance their teaching methods for these concepts.

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Homework Statement


Make the appropriate change of variables and evaluate \int\int _R\(sin(9x^2+4y^2)}\;dA


Homework Equations



R is bounded by the ellipse 9x^2+4y^2=1

The Attempt at a Solution



I can't figure out what the substitution should be I tried u=9x^2 and v=4y^2 and that didn't work and I don't know where to go from here.
 
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How about u=3x and v=2y? Then switch to polar coordinates in u and v.
 
ohhh... ok thanks. I should have seen that.
 

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