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

Pythagorean Theorem

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


Logarithms

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


Calculus

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


Newton’s Law of Gravity

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


Complex Numbers

$$i^2=-1$$


Euler’s Formula for Polyhedra

$$V-E+F=2$$


Normal Distribution

$$\Phi(x)= \frac{1}{\sqrt{2\pi\rho}} e^{\frac{(x-\mu)^2}{2\rho^2}}$$


Wave Equation

$$\frac{\partial^2 u}{\partial t^2} = c^2 \frac{\partial^2 u}{\partial x^2}$$


Fourier Transform

$$f(\omega) = \int_{\infty}^{\infty}f(x)e^{-2\pi i x \omega} \text{d}x$$


$$\rho\left(\frac{d\text{v}}{dt} + \text{v} \cdot \text{v}\nabla \right) = -\nabla p + \nabla \cdot \text{T} + \text{f}$$


Maxwell’s Equations

$$\begin{aligned} &\nabla\cdot\mathcal{E} = 0 &\nabla\cdot\mathcal{H} = 0 \end{aligned}$$

$$\begin{aligned} &\nabla\times\mathcal{E} = - \frac{1}{c}\frac{\partial\mathcal{H}}{\partial t} &\nabla\times\mathcal{H} = - \frac{1}{c}\frac{\partial\mathcal{E}}{\partial t} \end{aligned}$$


Second Law of Thermodynamics

$$dS\geq0$$


Relativity

$$E=mc^2$$


Schrödinger’s Equation

$$ih \frac{\delta}{\delta t}\Psi = H\Psi$$


Information Theory

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


Chaos Theory

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


Black-Scholes Equation

$$\frac{1}{2}\sigma^2S^2 \frac{\delta^2 V}{\delta S^2} + rS \frac{\delta V}{\delta S} + \frac{\delta V}{\delta t} - rV = 0$$


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