\infty
\lambda
\alpha
\beta
\gamma
\Delta
\theta
\psi
\vec F
a\not=b
a \not\in \mathbb{Q}
\frac x {y+1}
\sqrt{a^2+b^2}
\lim_{x\right\infty} f(x)
\sum_{i=1}^n%20a_i
\int_{-\infty}^x f(t)dt
\Large%20A\%20=\%20\large\left(\begin{array}&a_{11}&a_{12}&\cdots&a_{1n}\\&a_{21}&a_{22}&\cdots&a_{2n}\\&a_{31}&a_{32}&\cdots&a_{3n}\end{array}\right)
\left(\sum a_i^2\right)^{1/2}
\lim_{\delta\rightarrow 0}\frac{f(x+\delta)- f(x)}{\delta}
\begin{matrix} a_{11} & 0 & \ldots & a_{1n}\\ 0 & a_{22} & \ldots & a_{2n}\\ \vdots & \vdots & \ddots & \vdots\\ 0 & 0 &\ldots & a_{nn} \end{matrix}