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!

Struggling to rearrange equation

  1. Nov 13, 2013 #1
    I'm trying to prove that


    My workings so far:
    put over common denominator,
    expand out,
    group up and cancel out,

    we need to make it equal to
    Last edited: Nov 13, 2013
  2. jcsd
  3. Nov 13, 2013 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Education Advisor

    You can't because they're not equal. It's more apparent when you rewrite each slightly:
    $$\frac{2cl}{c^2-u^2} = \frac{2cl}{c^2[1-(u/c)^2]} = \frac{2l}{c}\frac{1}{1-(u/c)^2}$$ and
    $$\frac{2l}{\sqrt{c^2-u^2}} = \frac{2l}{\sqrt{c^2[1-(u/c)^2]}} = \frac{2l}{c}\frac{1}{\sqrt{1-(u/c)^2}}$$
  4. Nov 13, 2013 #3


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    There's no law against plugging some numbers in! If you're not sure whether two expressions are equal, try some numbers and see! l = 1, u = 1 and c = 2 proves a lack of equality here.
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: Struggling to rearrange equation
  1. Rearranging equations (Replies: 1)

  2. Equation Rearrangement (Replies: 3)

  3. Rearranging equations? (Replies: 1)

  4. Rearranging equation (Replies: 28)