\[a² - 8a + 17 > 0\]
\[a^{2} - 8a + 16 + 1 > 0\]
\[(a - 4)^{2} + 1 > 0\]
\[(a - 4)^{2} \geq 0;\ \ 1 > 0 \Longrightarrow верно.\]