1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Double integral limits?

  1. Jan 21, 2014 #1
    1. The problem statement, all variables and given/known data

    ∫∫ydxdy over the triangle with vertices (-1,0), (0,2), (2,0)

    2. Relevant equations


    I did it like this and got the right answer:

    ∫dy ∫ydx

    this first:
    ∫ydx from x = (y-2)/2 to x = 2-y

    then ∫dy from y = 0 to y = 2

    I got 2 which is correct


    but when I tried another method, splitting them up across the y axis i got 8/3:

    I did I = A+B

    A = ∫dx∫ydy

    ∫ydy from y = 0 to y = 2x+2

    then I integrated from x = -1 to x =0 (I got 2/3)

    B = ∫dx∫ydy

    ∫ydy from y =0 to y = -x+2

    then I integrated wrt x from x = 0 to x = 2 (I got 2)

    so the second answer was 8/3


    Why was the second one wrong? I keep getting questions wrong because of the limits I choose! Could someone help me out please?




    3. The attempt at a solution
     
  2. jcsd
  3. Jan 21, 2014 #2

    LCKurtz

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Your limits look to be correct with both methods. Without you showing your calculations instead of just giving us your answers, we can't tell where your mistake is.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Double integral limits?
Loading...