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!

Homework Help: Multivariable Calculus - midterm questions

  1. Jun 9, 2015 #1
    I have two problems I need help with

    1. The problem statement, all variables and given/known data


    2,3. Answers and work are given

    In the surface integral problem, I do not understand how it sets it up for Method 1. (How does it go from integral of x2+y2 to 2/3 integral of x2+y2+z2

    For the "estimate the integral" problem, I do not understand why e(sinx cosx sinz) is considered a constant function.

    Also, any cramming advice for passing a computation multivariable calc test would be appreciated.
  2. jcsd
  3. Jun 9, 2015 #2
    Total integers, with symmetry limits have 2/3 ratio.
  4. Jun 9, 2015 #3
    Could you explain that with more detail. The phrases total integers and symmetry limits do not appear in my textbook and google isn't much help.
  5. Jun 9, 2015 #4
    Make integrations with independent variables.
    $$ \int_{-a}^{a}\int_{-a}^{a}\int_{-a}^{a}dxdydz \,\text{and}\, \int_{-a}^{a}\int_{-a}^{a}dxdy $$
    They are for cube but the ratio is the same for symmetric integration limits. To make the 2nd integral directlly have much more work.
  6. Jun 9, 2015 #5


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    By symmetry, each of the following integrals gives the same value.

    ##\displaystyle \ \iint_{S} x^2\, dA=\iint_{S} y^2\, dA=\iint_{S} z^2\, dA\ ##

    You will usually get better response if you can post the images of your work directly.

    Better yet, is to use LaTeX OR all the nice little symbols PF has provided for you.
  7. Jun 10, 2015 #6
    Thank you both, it makes sense.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted