Two Brownian values, both positive

Let $B_t$ be a standard Brownian motion. Find $\mathbb{P}[B_2 > 0,\ B_8 > 0]$ . The probability equals $\tfrac{1}{M}$ for an integer $M$ ; find $M$ .

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$(B_2,B_8)$ is jointly normal with mean $0$ . Find its correlation using $\operatorname{Cov}(B_s,B_t)=\min(s,t)$ .
Use the orthant formula $\mathbb{P}[X>0,Y>0]=\tfrac14+\tfrac{\arcsin\rho}{2\pi}$ with $\rho=\tfrac12$ .

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