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Homework Help: Electrostatic algebra

  1. Feb 3, 2010 #1
    1. The problem statement, all variables and given/known data

    I have a homework question on electrostatic seesaws. My problem is the algebra.

    2. Relevant equations

    I have been following another example and any guidance to help me proceed would be great.

    0= (2q Q)/(4πε_o r²)+(q Q)/(4πε_o r²)-m
    0= (3q Q)/(4πε_o r²)-m
    m=(3q Q)/(4πε_o r²)

    I don't understand line 2. I don't understand how part of the equation has cancelled out. I know there is a step missing so could anyone point me in the right direction.

    3. The attempt at a solution
  2. jcsd
  3. Feb 3, 2010 #2


    User Avatar
    Science Advisor
    Homework Helper

    There is no step missing.

    There are two fractions which are the same, therefore they can be added:
    [tex]\frac{2x}{y} + \frac{x}{y} = \frac{3x}{y}[/tex]
  4. Feb 3, 2010 #3
    Of course! Thank you compuchip x
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