In his book, In Pursuit of the Unknown: 17 Equations That Changed the World, Ian Stewart discusses each equation engagingly and practically…

$a^2 + b^2 = c^2$

$log{xy} = log{x} + log{y}$

$$\frac{\partial f}{\partial t} = \lim_{x\to\infty} = \frac{f{(t+h)}- f{(t)}}{h}$$

${F}_\text{gravity}=G\frac{m_{1}m_{2}}{r^{2}}$

$i^2=-1$

$dS\geq0$

$E=mc^2$

$H=-\sum p(x) + log{p(x)}$

$x_{t+1} = kx_t(1-x_i)$