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Thread: Composition of Two Functions

  1. January 9th 2008, 03:47 PM #1
    Macleef
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    Composition of Two Functions

    Given f(x) = -5x + 2 and g(x) = -x^2 + 3


    Find (g \circ f)(x):


    = g(f(x))

    = g(-5x + 2)

    = -(-5x + 2)^2 + 3

    = - (25x^2 + 4) + 3

    = -25x^2 - 4 + 3

    = -25x^2 - 1


    And textbook answer is (g \circ f)(x) = -25x^2 + 20x - 1


    I don't know how to get the "20x" ? Please help me !
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  2. January 9th 2008, 03:53 PM #2
    Plato
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    - \left( { - 5x + 2} \right)^2 = - \left( {25x^2 - 20x + 4} \right)
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