Consider a random variable $X$ that takes values $+1$ and $−1$ with probability $0.5$ each. The values of the cumulative distribution function $F(x)$ at $x = −1$ and $+1$ are
The Cumulative Distribution Function (CDF), of a real-valued random variable X, evaluated at x, is the probability function that X will take a value less than or equal to x.
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F(X) is the cumulative distribution function and let P is the probability and given X is random variable so
The formula for cumulative distribution function is F(X)=P(X<=x)
=0.5 + 0.5