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Quadratic Equation help

  1. Apr 28, 2012 #1

    I was going through some mechanics notes and came across this quadratic equation to solve for x. In my notes it is supposed to equal 3 however I do not get that result. I am not sure if I am simplifying it wrong or what. I am ending up with 2.12 for the positive value. Please let me know if you get 3 or 2.12 so that I know if the error is in my calculations or in my notes.

    http://img707.imageshack.us/img707/338/codecogseqno.gif [Broken]

    Thanks in advanced.
    Last edited by a moderator: May 5, 2017
  2. jcsd
  3. Apr 28, 2012 #2

    It must be some mistake in your notes: if you put [itex]x=3[/itex] in the given eq., one gets that the LHS is not an integer

    whereas the RHS is...

    Last edited by a moderator: May 5, 2017
  4. Apr 29, 2012 #3


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    Staff: Mentor

    Neither 3 nor 2.12 are roots of the equation as you wrote it.
  5. Apr 29, 2012 #4
    3 is correct if the LHS is amended to contain 144x2 rather than 144 + x2.
  6. Apr 29, 2012 #5
    um... I haven't done this in a while so forgive me for being simple.... but that's not an equation.

    if you put x=10 you end up with the equation 122=900, which isn't true.

    There's been some kind of mistake.
  7. Apr 29, 2012 #6

    No, that is too an equation. To solve it means to find out the numerical values of x that when substituted in the equation give

    a true equality. What you've shown above is that the numerical value x = 10 is not (one of the) a solution(s) of the equation.

  8. Apr 29, 2012 #7
    oh, ok, yes. Sorry engineering maths was a decade ago for me. It's amazing how quickly the knowledge vanishes.

    I reduced the original equation down to 0=-71.5x^2+900x-2628 and got 0=(x-4.604)*(x-7.984)
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