\[x² + kx - 16 = 0\ \ \ \ \ \ и\ \ \ \ x_{1} = - 2\]
\[x_{1} + x_{2} = - k \Longrightarrow - 2 + 8 =\]
\[= - k \Longrightarrow 6 = - k \Longrightarrow k = - 6\]
\[x_{1} \cdot x_{2} = - 16 \Longrightarrow - \ 2 \cdot x_{2} =\]
\[= - 16 \Longrightarrow x_{2} = 8.\]