6. If $\sin \alpha+\sin \beta=1, \cos \alpha+\cos \beta=0$, then $\cos 2 \alpha+\cos 2 \beta=$
6. 1 . $\sin \alpha=1-\sin \beta, \cos \alpha=-\cos \beta$, squaring and adding the two equations yields $\sin \beta=\frac{1}{2}, \sin \alpha=\frac{1}{2}$, so $\cos 2 \alpha=$ $\cos 2 \beta=1-2 \sin ^{2} \beta=1-2 \sin ^{2} \alpha=\frac{1}{2}$. Therefore, $\cos 2 \alpha+\cos 2 \beta=1$.