๐Ÿ“ Math

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Inline Formula

When aโ‰ 0a \ne 0, there are two solutions to ax2+bx+c=0ax^2 + bx + c = 0 and they are
x=โˆ’bยฑb2โˆ’4ac2a.x = {-b \pm \sqrt{b^2-4ac} \over 2a}.

The Lorenz Equations

xห™=ฯƒ(yโˆ’x)yห™=ฯxโˆ’yโˆ’xzzห™=โˆ’ฮฒz+xy\begin{align} \dot{x} & = \sigma(y-x) \\ \dot{y} & = \rho x - y - xz \\ \dot{z} & = -\beta z + xy \end{align}

The Cauchy-Schwarz Inequality

(โˆ‘k=1nakbk)โ€‰โฃโ€‰โฃ2โ‰ค(โˆ‘k=1nak2)(โˆ‘k=1nbk2)\left( \sum_{k=1}^n a_k b_k \right)^{\!\!2} \leq \left( \sum_{k=1}^n a_k^2 \right) \left( \sum_{k=1}^n b_k^2 \right)

A Cross Product Formula

V1ร—V2=โˆฃijkโˆ‚Xโˆ‚uโˆ‚Yโˆ‚u0โˆ‚Xโˆ‚vโˆ‚Yโˆ‚v0โˆฃ\mathbf{V}_1 \times \mathbf{V}_2 = \begin{vmatrix} \mathbf{i} & \mathbf{j} & \mathbf{k} \\ \frac{\partial X}{\partial u} & \frac{\partial Y}{\partial u} & 0 \\ \frac{\partial X}{\partial v} & \frac{\partial Y}{\partial v} & 0 \\ \end{vmatrix}

The probability of getting (k)\left(k\right) heads when flipping (n)\left(n\right) coins is:

P(E)=(nk)pk(1โˆ’p)nโˆ’kP(E) = {n \choose k} p^k (1-p)^{ n-k}

An Identity of Ramanujan

1(ฯ•5โˆ’ฯ•)e25ฯ€=1+eโˆ’2ฯ€1+eโˆ’4ฯ€1+eโˆ’6ฯ€1+eโˆ’8ฯ€1+โ€ฆ\frac{1}{(\sqrt{\phi \sqrt{5}}-\phi) e^{\frac25 \pi}} = 1+\frac{e^{-2\pi}} {1+\frac{e^{-4\pi}} {1+\frac{e^{-6\pi}} {1+\frac{e^{-8\pi}} {1+\ldots} } } }

A Rogers-Ramanujan Identity

1+q2(1โˆ’q)+q6(1โˆ’q)(1โˆ’q2)+โ‹ฏ=โˆj=0โˆž1(1โˆ’q5j+2)(1โˆ’q5j+3),forย โˆฃqโˆฃ<1.1 + \frac{q^2}{(1-q)}+\frac{q^6}{(1-q)(1-q^2)}+\cdots = \prod_{j=0}^{\infty}\frac{1}{(1-q^{5j+2})(1-q^{5j+3})}, \quad\quad \text{for $|q|<1$}.

Maxwell's Equations

โˆ‡ร—Bโƒ—โˆ’โ€‰1cโ€‰โˆ‚Eโƒ—โˆ‚t=4ฯ€cjโƒ—โˆ‡โ‹…Eโƒ—=4ฯ€ฯโˆ‡ร—Eโƒ—โ€‰+โ€‰1cโ€‰โˆ‚Bโƒ—โˆ‚t=0โƒ—โˆ‡โ‹…Bโƒ—=0\begin{align} \nabla \times \vec{\mathbf{B}} -\, \frac1c\, \frac{\partial\vec{\mathbf{E}}}{\partial t} & = \frac{4\pi}{c}\vec{\mathbf{j}} \\ \nabla \cdot \vec{\mathbf{E}} & = 4 \pi \rho \\ \nabla \times \vec{\mathbf{E}}\, +\, \frac1c\, \frac{\partial\vec{\mathbf{B}}}{\partial t} & = \vec{\mathbf{0}} \\ \nabla \cdot \vec{\mathbf{B}} & = 0 \end{align}