Let T $T$ be an algebraic torus defined over Q$\mathbb Q$, $T_infinity$ T_\infty$ be its reals real points and $\pi_0(T_infinity)$ \pi_0(T_\infty)$ be the group of connected components of $T_infinity$. T_\infty$.
Why is the homomorphism $T(Q)\ra T(\mathbb Q)\to \pi_0(T_infinity)$ pi_0(T_\infty)$ surjective?
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