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Find zeros of quadratic equation

  1. Jun 21, 2011 #1
    1. The problem statement, all variables and given/known data
    Find the zeros of the quadratic equation?


    2. Relevant equations

    P(x)=4(x+7)^2+(x+7)-3

    3. The attempt at a solution

    I substituted and made it 4u^2+u-3 ?? Then after that I factor then back substitute?? I'm not sure how to back substitute tho.
     
  2. jcsd
  3. Jun 22, 2011 #2
    Think about what u is equal to when you make the substitution. If you have that and the value for u, finding x should be straightforward.
     
  4. Jun 22, 2011 #3

    gb7nash

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    Homework Helper

    What's the equation for u in terms of x? Once you have this, solve for x in the equation and plug in the values you got for u.
     
  5. Jun 23, 2011 #4
    You did a change of variables. You substituted u for x where u = x+7 to get the equation

    [tex] f(u) \, = \, 4u^{2} \, + \, u \, - \, 3 \, = \, 0[/tex]

    solve for u in the above expression then use u = x + 7 to find x for each u.

    i.e. since u = x+7 then x = u - 7 gives you x.
     
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