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Homework Help: I need help with two problems.

  1. Feb 20, 2006 #1
    If f(x)=x^2-3x and g(x)=in square root of x+6, solve for x if f(g{x))=30

    Also, factor this expression and simplify if necessary: (x+5)^2+6(x+5)(x-4)

    Thanks.
     
  2. jcsd
  3. Feb 20, 2006 #2
    What have you tried so far? What are you having trouble with?
     
  4. Feb 20, 2006 #3
    For the first one, I got to, x+6 - 3(square root of x+6) = 30 lol

    I don't know what to do next, I think I'm supposed to get rid of the three, but I'm not sure how.
     
  5. Feb 20, 2006 #4
    You can make a substitution to end up with a quadratic equation,

    let u = square root of (x+6)

    so you end up with

    u2 - 3u = 30

    You can then solve for u and thn substitue back to solve for x.
     
  6. Feb 21, 2006 #5

    VietDao29

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    Homework Helper

    For the second one, you may want to factor (x + 5) out.
    (x + 5)2 + 6(x + 5)(x - 4) = (x + 5) (x + 5 + 6(x - 4)) = ...
    Can you go from here? :)
     
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