Friday, 13 January 2017

calculus - Prove that intRfrac11x2y2,dx,dy=suminftyn=0frac1(2n+1)2



The region R is the unit square with corners at (0,0),(1,0),(0,1) and (1,1).




The idea is to consider the geometric series.



Any help would be appreciated. Thank you


Answer



I collect all hints and write down the answer.




  1. We use the formula for sum of a geometric series as following
    11x2y2=1+x2y2+x4y4+.

  2. Then we have
    R11x2y2dxdy=Rn=0x2ny2ndxdy=n=0Rx2ny2ndxdy.

  3. And Rx2ny2ndxdy=1010x2ny2ndxdy=1/(2n+1)2.

  4. Finally
    R11x2y2dxdy=n=01(2n+1)2.


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