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Find the coefficient - calculus questions

  1. Jul 21, 2009 #1
    1:
    If g(x) = 2x^2 – 5x then g(2+h) =

    my working

    2(2+h)^2 -5(2+h)
    ( 2((2+h)*(2+h)) ) - 5(2+h)
    2(4 + h^2 + 4h) - 10 -5h
    8 + 2h^2 + 8h - 10 -5h

    -2 + 3h + 2h^2

    2:
    Find the coefficient of x in (2x – 7)^2.
    isn't it 2?
     
  2. jcsd
  3. Jul 21, 2009 #2
    #1 looks correct.
    #2 you'll have to expand it first!
     
  4. Jul 21, 2009 #3
    Find the coefficient of x in (2x – 7)2.

    2x-7 * 2x-7
    4x^2 - 14x - 14x + 49

    4x^2 - 28x + 49

    coefficient is 4-28?
    so -24?
    or 4, or 28

    i'm pretty sure it's 4, because it's infront of the x^2, but the 28 infront of x could also be a coefficient?
     
  5. Jul 21, 2009 #4

    rock.freak667

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    Coefficient fof x is the number in front of x....so in 4x^2 + (- 28)x + 49 what is that?
     
  6. Jul 21, 2009 #5
    there is a 4 in front of the x^2,
    and -28 infront of the x.

    if you meant the number infront of just the x, then it's -28
    if you meant the number infront of the x, in x^2 then it's 4

    which one do i choose? the power functioned x or the x without it?

    i'm assuming it's the x without it because if there were more functions, like a cubic polynomial, with like ax^4 + bx^3 + cx^2 + dx + e, then it'd get confusing

    so -28 is my awnser?
     
  7. Jul 21, 2009 #6

    rock.freak667

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    Yes.


    But if you had

    ax3+bx2+cx+d

    The coefficient of x3 is a
    The coefficient of x2 is b
    The coefficient of x is c

    and so forth.
     
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