Simple inline $a = b + c$.
$$\frac{\partial u}{\partial t}
= h^2 \left( \frac{\partial^2 u}{\partial x^2} +
\frac{\partial^2 u}{\partial y^2} +
\frac{\partial^2 u}{\partial z^2}\right)$$
$${a * b}$$
$$\left( \frac{1}{2} \right)$$
$$\int_0^1 x \, dx= $$
$$f(a) = \frac 1 {2\pi i} \oint_{\gamma}
\frac{f(z)} {z - a} dz$$