# finding the p.m.f

• October 6th 2010, 06:09 PM
calculuskid1
finding the p.m.f
Let the pmf of X be defined by f(x)=6/((pi^2)(x^2)), x=1,2,3....

show that E(X) does not exist (Can you show that f(x) is a p.mf.?)

And I know that x^-2 converges to Pi^2/6 ..
• October 6th 2010, 06:41 PM
mr fantastic
Quote:

Originally Posted by calculuskid1
Let the pmf of X be defined by f(x)=6/((pi^2)(x^2)), x=1,2,3....

show that E(X) does not exist (Can you show that f(x) is a p.mf.?)

And I know that x^-2 converges to Pi^2/6 ..

$\displaystyle E(X) = \sum_{x = 1}^{+\infty} x f(x)$. Does this series converge ....?
• October 10th 2010, 07:33 AM
matheagle
Quote:

Originally Posted by calculuskid1
Let the pmf of X be defined by f(x)=6/((pi^2)(x^2)), x=1,2,3....

show that E(X) does not exist (Can you show that f(x) is a p.mf.?)

And I know that x^-2 converges to Pi^2/6 ..

I assume you mean the sum converges to $\pi^2/6$