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I am doing a problem with PDF's and this integral is a roadblock.

I have $f(x)=\dfrac{200}{(x+10)^3}$ where $x>0$ and have solved that $\mathbb{E}(X)=10$.

I am working on finding $\mathbb{E}(X^2)$ and so far have $\mathbb{E}(X^2)=\displaystyle \int_0^\infty \frac{200x^2}{(x+10)^3}$.

How do I go about showing that $\mathbb{E}(X^2)$ diverges? I tried substitution but it doesn't seem to work

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    Note that $\frac{x^2}{(x+10)^3}\sim \frac{1}{x}$2012-03-19

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