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Basic manipulating equation algebra problem?

  1. Oct 19, 2012 #1
  2. jcsd
  3. Oct 19, 2012 #2

    NascentOxygen

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    Staff: Mentor

    Subtract 2mgh from both sides, then subtract 2mgx from both sides

    You can do it that way, too. Now multiply every term on both sides by -1
     
  4. Oct 19, 2012 #3
    why do we need to mult both side by -1?
     
  5. Oct 19, 2012 #4

    NascentOxygen

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    Staff: Mentor

    That gets you the equation that you were expecting to see, but by a different route.
     
  6. Oct 19, 2012 #5


    but what if you dont know the correct equation?

    If i was doing this problem from scratch (without solution manuel)

    I wouldnt have known this equation [0 = 2mgh + 2mgx - kx^(2)] was wrong because algebraically, i am correct.

    is it like instincts from reading the problem to know what kind of equation to expect or something???
     
  7. Oct 19, 2012 #6
    Do you want to solve for x or what?
     
  8. Oct 19, 2012 #7
    yes.
     
  9. Oct 19, 2012 #8
    Okay, now you got kx^(2) - 2mgh - 2mgx = 0 so you can use the quadratic formula to solve for x.
     
  10. Oct 19, 2012 #9

    NascentOxygen

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    Staff: Mentor

    It's not wrong. It's perfectly correct.

    In general, it is customary to arrange the terms in decreasing degree, and with the leading term having a positive coefficient, e.g., x2 - 4x + 3 = 0

    But this is just for appearances (and it makes it easier to comprehend), it's not wrong if you don't do this.

    Multiplying both sides does not change anything material. If you do the same thing to both sides of an equation, you change nothing.
     
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