\(\left\{{}\begin{matrix}x_1+x_2=2\\x_1x_2=-1\end{matrix}\right.\)
8: \(=\dfrac{x_1^2+x_2^2}{\left(x_1\cdot x_2\right)^2}=\dfrac{2}{1}=2\)
9: \(=\left(x_1+x_2\right)^3-3x_1x_2\left(x_1+x_2\right)=2^3-3\cdot\left(-1\right)\cdot2=8+6=14\)
16: \(=\sqrt{\left(x_1+x_2\right)^2-4x_1x_2}=\sqrt{2^2-4\cdot\left(-1\right)}=\sqrt{4+4}=2\sqrt{2}\)