emph

https://math.meta.stackexchange.com/questions/5020/mathjax-basic-tutorial-and-quick-reference

Default font size. Different font size. Bold text. bold text. italic text. Italic text. Underlined text.

At first, we sample $$f(x)$$ in the $$N$$ ($N$ is odd) equidistant points around $$x^*$$:

$f_k = f(x_k),\: x_k = x^*+kh,\: k=-\frac{N-1}{2},\dots,\frac{N-1}{2}$

where $$h$$ is some step.

Then we interpolate points $$(x_k,f_k)$$ by polynomial

\label{eq:poly} \tag{1}
P_{N-1}(x)=\sum_{j=0}^{N-1}{a_jx^j}

Its coefficients $$a_j$$ are found as a solution of system of linear equations:
\label{eq:sys} \tag{asdf}

\label{eq:sys2} \tag{asdf2}

Backslash left and right parentheses:

$\left( \frac{1}{2} \right) \qquad ( \frac{1}{2} ) \\ ( \frac{1}{2} )$

$$1 \quad \frac ab \quad 2 \quad \frac{c}{d} \quad 3 \quad {e \over f} \quad 4 \quad {}^g/_h \quad 5 \quad i/j \quad 6 \quad$$

$$1+1=2 \textrm{ centered equation } 1+1=2$$

$$1+1=2 \textrm{ left equation } 1+1=2$$

\begin{align}
1 + 1 & = 2.00000000 \textrm{ aligned to a specific character}\\
& = 2.0 \\
& ? 2.0000000000000000 \\
& | 1.99999999999 \\
\end{align}

Here are references to existing equations: \ref{eq:poly}, \eqref{eq:sys}.
Here is reference to non-existing equation \eqref{eq:unknown}.

X=
\begin{cases}
0, & \text{if}\ a=1 \\
1, & \text{otherwise}
\end{cases}

$$\lim_{x\to 1}$$

$$\lim_{x\to 1}$$

$$default, \it Italics, \bf bold bold, \textbf {bold bold}, \sf sans serif, \tt typewriter, \rm default Roman, \underline {underline}$$

For bold, use \boldsymbol: $$X \boldsymbol{X}$$

For greater than and less than, use \gt $$\gt$$ and \lt $$\lt$$, \geq $$\geq$$ and \leq $$\leq$$.

$$horizontal spacing: nospace, one space, many spaces, backslash \ comma \, ! \! > \> : \: ; \; enspace \enspace quad \quad qquad \qquad end$$

$$hskip1point \hskip1pt hskip2point \hskip 2pt hskip10point \hskip10pt hskip20point \hskip 20pt hskip3point \hskip 3pt 1ex \hspace{1ex} 1em \hspace{1em} 2em \hskip2em lengthofasdf \hphantom{<asdf>} backslash \ tilde ~ end$$

$$\tiny tiny$$

$$default$$

$$\scriptsize scriptsize, \small small, \normalsize normalsize \ or \ default, \large large$$

$$\normalsize normalsize \ or \ default, \large large$$

$$\Large Large \LARGE LARGE \huge huge \Huge Huge1$$

$$\Large \LARGE \huge \Huge Huge2$$

$$\Huge Huge3$$

$$\LARGE LARGE \huge huge \Huge Huge4$$

$$\huge huge \Huge Huge5$$

$$\Large Large1 \Large Large2 \Large Large3 \Large Large4$$

$$\LARGE LARGE1 \LARGE LARGE2 \LARGE LARGE3 \LARGE LARGE4$$

$$\huge huge1 \huge huge2 \huge huge3 \huge huge4$$

$$\Huge Huge1 \Huge Huge2 \Huge Huge3 \Huge Huge4$$

Many blank lines:

Missing \right:

$\left( \frac{1}{2} \right) \ as \qquad \ df \left( \frac{1}{2} ) \ jkl$