\[ x = {-b \pm \sqrt{b^2-4ac} \over 2a} \tag{1} \]

\[ \int_{-\infty}^{\infty}\exp(-x^2) dx = \frac{1}{\sqrt{2\pi}} \tag{2} \]

\[ \frac{\pi}{2} = \left( \int_{0}^{\infty} \frac{\sin x}{\sqrt{x}} dx \right)^2 = \sum_{k=0}^{\infty} \frac{(2k)!}{2^{2k}(k!)^2} \frac{1}{2k+1} = \prod_{k=1}^{\infty} \frac{4k^2}{4k^2 - 1} \tag{3} \]