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Homework Help: Continuous Random Variable question

  1. Mar 27, 2008 #1
    1. The problem statement, all variables and given/known data
    Problem statement is underlined. Having problems to prove this.

    2. Relevant equations

    F(x) = ∫ f(x) dx
    Question relating to cumulative distributive function. Part ii requiring to relate cumulative distributive function to probability density function.

    3. The attempt at a solution

    CRV_t44_q1_1.png
    CRV_t44_q1_2.png


    Why I'm stuck =>
    (4x³ - 4x² - 39x - 36) ≠ (3 + 2x)²(4 - x)
    (3 + 2x)²(4 - x) = (-4x³) - 4x² - 39x + 36

    Stuck after that as the positive and negative signs seems swapped. Checked again and nothing seems to change.

    Is this due to a faulty question or I'm missing out something vital?
     
    Last edited: Mar 27, 2008
  2. jcsd
  3. Mar 28, 2008 #2

    tiny-tim

    User Avatar
    Science Advisor
    Homework Helper

    Hi PuzzledMe! :smile:

    You can check which is right by putting x = 4: that should give 0.

    (4x³ - 4x² - 39x - 36) = 256 - 64 - 156 - 36 = 0
    (-4x³) - 4x² - 39x + 36 = -256 -64 -156 + 36 ≠ 0.

    So your expansion of (3 + 2x)²(4 - x) must be wrong!

    And it is … try again! :smile:
     
  4. Apr 9, 2008 #3
    Thanks tim for the tireless response, I've solved it from here, sorry about the late reply but I owe you one!
     
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