TeX джерело:

1)\quad \frac{\begin{array}{l}3 < 4\\ \times \\5 < 6\end{array}}{\begin{array}{l}3 \cdot 5 < 4 \cdot 6\\\;\;15 < 24\end{array}};\quad 2)\quad \frac{\begin{array}{l}7 > 3\\ \times \\3 > 1\end{array}}{\begin{array}{l}7 \cdot 3 > 3 \cdot 1\\\;\;21 > 3\end{array}};\quad 3)\quad \frac{\begin{array}{l}x + y > x\\ \times \\x - y > y\end{array}}{\begin{array}{l}(x + y)(x - y) > xy\\\;\;\;\;{x^2} - {y^2} > xy\end{array}}