$X(t)$ is a Gaussian WSS process with $E${$X(t)$}$=0$ and $R(\tau)=2e^{-2|\tau|}$
1.Find the $P${$X(t) \le 3$},and just express it as Q-function
About the first question,according to $X(t)$ is WSS , i only know it can be fouriered to know its power , but i don't know how to calculate its probability when i know its autocorrelation , is there a relation between autocorrelation and probability ?
2.Determine $E${$(X(t+1)-X(t-1))^2$}
About the second question,when i express this formula, \begin{align} E[(X(t+1)-X(t-1))^2] & = E[X^2(t+1)+X^2(t-1)-2X(t+1)X(t-1)] \\ & = E[X^2(t+1)]+E[X^2(t-1)]-E[2X(t+1)X(t-1)] \end{align}
I think i can regard $E[2X(t+1)X(t-1)]$ as $2$ times of its autocorrelation when $\tau = 2$ , but i don't know how to solve $E[X^2(t+1)]$ and $E[X^2(t-1)]$ . It seems that i can use the variance , $\sigma ^2 = E[X^2(t)]-E^2[X(t)]$ , to know what is $E[X^2(t)]$ , but i don't know wheather i can also know $E[X^2(t+1)]$ and $E[X^2(t-1)]$ or not when i know $E[X^2]$ first