1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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!
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook




Loading...