\[\ a² + 1 \geq 2 \cdot (3a - 4)\]
\[a^{2} + 1 \geq 6a - 8\]
\[a^{2} - 6a + 9 \geq 0\]
\[(a - 3)^{2} \geq 0 \Longrightarrow ч.т.д.\]
\[x > y\]
\[\ 13x > 13y\]