Let $(S,F,P)$ be probability space and $X :S \rightarrow \mathbb{R}$ be random variable with mean 0 and variance 1.
Let $c \geq 0$.
I want to show that $P(X \geq c) \leq \frac{1}{1+c^2}.$
I already know Chebychev inequality $P(X\geq) \leq 1/c^2$ when $c > 0$.
If this inequality holds, $1/1+c^2$ will be better estimates.
Could you help me?