$8 \sqrt{2}$ 14. Let $x_{1}, X_{2}, X_{3}$ be random variables with equal variances but with correlation coefficients $ ho_{12}=\frac{3}{10}, ho_{13}=\frac{1}{2}$ and $ ho_{23}=\frac{1}{5} $ Find the correlation coefficient $ ho_{12}$ of the linear functions $Y=X_{1}+x_{2}$ and $Z=X_{2}+x_{3} \cdot ho_{Y Z}=\frac{5} {\sqrt{39}}$ SP.AS. 11371