9. Given $\sin x+\sin y=0.6, \cos x+\cos y=0.8$. Then $\cos x \cdot \cos y=$
9. $-\frac{11}{100}$

By squaring and then adding the two given equations on both sides, we can get $\cos (x-y)=-\frac{1}{2}$; by transforming the left side of the two given equations into products and then dividing them, we can get $\operatorname{tg} \frac{x+y}{2}=\frac{3}{4}$, from which we obtain $\cos (x+y)=\frac{7}{25}$. Using $\cos x \cos y=\frac{1}{2}[\cos (x+y)+\cos (x-y)]$, we can get.