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$E = mc^2$ $\frac{a}{b}$ $a^2 + b^2 = c^2$ $$\int_{-\infty}^{\infty} e^{-x^2} , dx = \sqrt{\pi}$$ $$f(x) = \begin{cases} \frac{x^2 - 1}{x - 1} & \text{if } x \neq 1 \ 2 & \text{if } x = 1 \end{cases}$$ $$\begin{pmatrix} a & b \ c & d \end{pmatrix}^{-1} = \frac{1}{ad - bc} \begin{pmatrix} d & -b \ -c & a \end{pmatrix}$$ $$\begin{aligned} (x + y)^2 &= (x + y)(x + y) \ &= x^2 + xy + yx + y^2 \ &= x^2 + 2xy + y^2 \end{aligned}$$