$f(x_1) = sin(x_1)^2$
$$f(x)=
\begin{cases}
0& \text{x=0}\\
1& \text{x!=0}
\end{cases}$$
$$
\sum_{i=0}^N\int_{a}^{b}g(t,i)\text{d}t
$$
$$\begin{bmatrix}
{a_{11}}&{a_{12}}&{\cdots}&{a_{1n}}\\
{a_{21}}&{a_{22}}&{\cdots}&{a_{2n}}\\
{\vdots}&{\vdots}&{\ddots}&{\vdots}\\
{a_{m1}}&{a_{m2}}&{\cdots}&{a_{mn}}\\
\end{bmatrix}$$
$$\begin{cases}
a_1x+b_1y+c_1z=d_1\\
a_2x+b_2y+c_2z=d_2\\
a_3x+b_3y+c_3z=d_3\\
\end{cases}
$$