Matrices:
[[a,b],[c,d]] yields ${\displaystyle \left[\begin{array}{cc}a& b\\ c& d\end{array}\right]}$

Column Vectors:
((a),(b)) yields ${\displaystyle \left(\begin{array}{c}a\\ b\end{array}\right)}$

Augmented Matrices:
[[a,b,|,c],[d,e,|,f]] yields ${\displaystyle \left[\begin{array}{ccc}a& b& c\\ d& e& f\end{array}\right]}$

System of Equations:
{(2x,+,17y,=,23),(x,-,y,=,5):} yields ${\displaystyle \{\begin{array}{lllll}2x& +& 17y& =& 23\\ x& -& y& =& 5\end{array}}$

Complex Subscripts:
lim_(N->oo) sum_(i=0)^N yields ${\displaystyle \underset{N\to \infty }{lim}\sum _{i=0}^N}$

Subscripts Before Superscripts:
int_0^1 f(x)dx yields ${\displaystyle {\int }_0^{1}f\left(x\right)dx}$

Derivatives:
f'(x) = dy/dx yields ${\displaystyle f\prime \left(x\right)=\frac{dy}{dx}}$
(dq)/(dp) yields ${\displaystyle \frac{dq}{dp}}$

Overbraces and Underbraces:
ubrace(1+2+3+4)_("4 terms") yields ${\displaystyle \underset{\text{4 terms}}{\underbrace{1+2+3+4}}}$.
obrace(1+2+3+4)^("4 terms") yields ${\displaystyle \stackrel{\text{4 terms}}{\overbrace{1+2+3+4}}}$.

Circle Arcs:
overset(frown)(AB) yields ${\displaystyle \stackrel{⌢}{AB}}$