Find E(X) given the moment generating function(adsbygoogle = window.adsbygoogle || []).push({});

M_X (t) = 1 / (1-t^2)

for |t| < 1.

(The pdf is f(x) = 0.5*exp(-|x|), for all x, so graphically you can see that E(X) should be 0.)

----

I know that E(X) = M ' _X (t) = 0

BUT M ' _X (t) = 2x / (1-x^2)^2 which is indeterminate at 0 so maybe you need L'Hopital's rule or something but I can't get it to work. How do you do this?

**Physics Forums | Science Articles, Homework Help, Discussion**

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Finding expected value from moment generating function

**Physics Forums | Science Articles, Homework Help, Discussion**