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Possible Duplicate:
Proof that $x \Phi(x) + \Phi'(x) \geq 0$ $\forall x$, where $\Phi$ is the normal CDF

Let Z be a standard normal random varible. How to prove that:

$$P(Z>t)>\frac{1}{\sqrt{2\pi}}\frac{t}{t^{2}+1}e^{-\frac{t^{2}}{2}} $$

Thanks for helping me.

Community
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John
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  • I recommend closure as a duplicate of many previous questions e.g. this one – Dilip Sarwate Dec 08 '11 at 20:32
  • Thanks. And I have edited my question to another part of my question. Could you have a look? – John Dec 08 '11 at 20:57
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    In the future, it's better not to edit a question to change it to a different question. It causes confusion with comments, votes, etc that are no longer relevant. You should ask a new question instead. – Nate Eldredge Dec 08 '11 at 22:38

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