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Homework Help: Find the volume of the region bounded by the planes (Multiple Integration).

  1. Apr 4, 2012 #1

    s3a

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    1. The problem statement, all variables and given/known data
    Find the volume of the region bounded by the planes 7x + 6y + 8z = 9, y = x, x = 0, z = 0.

    2. Relevant equations
    Multiple integration.

    3. The attempt at a solution
    My attempt at a solution is attached. To test, I computed the answer with Wolfram Alpha which yielded an incorrect answer of 243/5488.

    Any help in solving this problem would be greatly appreciated!
    Thanks in advance!
     

    Attached Files:

  2. jcsd
  3. Apr 5, 2012 #2

    HallsofIvy

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    Science Advisor

    You have decided to integrate with respect to z, then y, then x so look at the projection down to the plane z= 0. When z= 0 the plane 7x+ 6y+ 8z= 9 becomes the line 7x+ 6y= 9 which intersects the x-axis at (9/7, 0) and the y-axis at (0, 3/2).

    So x will range from 0 to 9/7 and, for each x, y will range from 0 to (9- 7x)/6. In your attachment, you have the equation y= (9- 7x)/6 but, for some reason, you show the upper limit of the "dy" integral as just x rather than (9- 7x)/6.
     
  4. Apr 5, 2012 #3

    s3a

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    My latest triple integral (in the image I just attached) is wrong. Did I misinterpret what you said?
     

    Attached Files:

  5. Apr 6, 2012 #4

    s3a

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    I re-attempted the problem based on some new stuff I've learned but I still get a wrong answer. (I attached my latest work.) Could you please tell me what's wrong in the setup?
     
  6. Apr 7, 2012 #5
    I've been reading how to do this, you want to take a double integral of your plane as follows:

    $$ \int_0^{\frac{9}{7}} \int_0^{\frac{9-7x}{6}} \frac{9-7x-6y}{8} dy dx $$
     
    Last edited: Apr 7, 2012
  7. Apr 7, 2012 #6

    s3a

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