$$ \sum_a^b x + \sqrt{\frac{x^2}{k+1}}\qquad x^{\frac{2}{k+1}}\qquad \frac{\partial^2f}{\partial x^2} x = a_0 + \frac{1}{a_1 + \frac{1}{a_2 + \frac{1}{a_3 + a_4}}} \sqrt[n]{ab}
$$
$$  \begin{pmatrix} a_{11} & a_{12} & a_{13}\\ a_{21} & a_{22} & a_{23}\\ a_{31} & a_{32} & a_{33} \end{pmatrix} $$