1. Not finding help here? Sign up for a free 30min 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!

Marginal Density Fx (x)

  1. Aug 15, 2010 #1
    1. The problem statement, all variables and given/known data

    Calculate the marginal density of fx (x).
    Fx,y (x,y) = double integral of 4x.e^(x+y) when 0<x<y, 0 otherwise.


    2. Relevant equations



    3. The attempt at a solution

    i set up the equation as fx (x) = integral from x up to infinity of 4x.e^(x+y) dy

    i get 4x [e^(x+y)] from x to infinity,

    thats when the problem arises as whatever i do there's always infinity in the question.

    I'm told the answer is 4x.e^(-2x)

    any help would be really appreciated.
    thanks.
     
  2. jcsd
  3. Aug 15, 2010 #2

    lanedance

    User Avatar
    Homework Helper

    are you sure you haven't missed a minus sign in the original distribution>
    [tex] f_{X,Y} (x,y)dxdy = 4xe^{-(x+y)}dx dy [/tex]

    would make more sense, the distrubution you gave is unbounded
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook