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: Change of Variables - Help!

  1. Sep 21, 2009 #1
    1. The problem statement, all variables and given/known data
    using change of variables, find the region bounded by
    y = x, y = 2x, xy = 1, xy=2

    2. Relevant equations

    3. The attempt at a solution
    i know i have to introduce the variables u, v
    the problem is i don't understand how to introduce them
    i tried read the textbook but the examples all introduce the new variables for you

    i think i understand the steps that follow, im just stuck at the beginning
  2. jcsd
  3. Sep 21, 2009 #2


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Well, you would like your uv integral to have constant limits if possible. You have xy=1 and xy=2 so that certainly suggests setting u or v = xy. If you use v, then v will go from 1 to 2.

    Now can you see how to choose u so that y = x and y = 2x give you constant limits for u?
  4. Sep 21, 2009 #3
    i guess y/x?
    that'll give me 1 to 2 as well?
  5. Sep 21, 2009 #4


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Good guess. I hope it wasn't a pure guess. You don't have to ask about the limits. Look at the equations. And plot your uv region.
  6. Sep 21, 2009 #5
    i vaguely remembered a similar example the prof did, i missed how he had chosen u and v, which resulted in my confusion

    thank you so much for the help!
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook