## Building math structures

Variables and constants are simple. But there are more complex objects, like binomial coefficients, vectors, and matrices. We shall figure out how to typeset such structures. Let's begin with simple arrays.

### Creating arrays

For arranging math expressions within a surrounding expression, there's the **array** environment. We use it exactly like a `tabular`

environment. However, it requires math mode and all of its entries are made using the math mode as well.

For example, by using variable sized parentheses around the array:

\[ A = \left( \begin{array}{cc} a_{11} & a_{12} \\ a_{21} & a_{22} \end{array} \right) \]

### Writing binomial coefficients:

Binomial coefficients and matrices may be typeset using an array together with delimiters. However, the `amsmath`

package provides shorter commands, for instance, `\binom`

for binomial coefficients:

\binom{n}{k} = \frac{n!}{k!(n-k)!}

### Typesetting matrices

As you might expect now of `amsmath`

, there are many special...