Katex test

$$\begin{equation}\int_0^\infty e^{-x^2}\,dx = \frac{\sqrt{\pi}}{2}\end{equation}$$ \begin{align}\sin^2\theta + \cos^2\theta &= 1 \\nabla \times (\nabla \times \mathbf{V}) &= \nabla(\nabla \cdot \mathbf{V}) - \nabla^2\mathbf{V}\end{align}\begin{cases}n! & n \geq 0 \\infty & n < 0\end{cases}\begin{bmatrix}1 & 2 & 3 \4 & 5 & 6 \7 & 8 & 9\end{bmatrix}\begin{vmatrix}a & b \\c & d\end{vmatrix} = ad - bc$$ \sum_{k=1}^n k = \frac{n(n+1)}{2} $$$$\frac{d}{dx}\left(\frac{1}{1+x^2}\right)=-\frac{2x}{(1+x^2)^2}$$