# Algebra II Terms

## Get down with the lingo

### Cramer's Rule

A matrix-style method for solving square systems of equations. We bust out a coefficient matrix, track down the determinant*D*, and swap out each variable column for a constant column to get the new determinants

*D*and

_{x}*D*. To solve for

_{y}*x*, divide

*D*by

_{x}*D*. To solve for

*y*, divide

*D*by

_{y}*D*. It's got more letters than a Chekhov play, but it's super useful.

### Determinant

While it sounds like the name of some cheesy product from an "As Seen On TV" infomercial, it's actually a special number derived from a square matrix. It's useful to know sometimes, and it's written as |*A*| =

*ad*–

*bc*for a 2 × 2 matrix.

### Entries

Each number or variable inside the brackets of a matrix.### Identity Matrix

The matrix version of the number 1, i.e.*the best matrix*. At least, it thinks that it's #1. More objectively speaking, it's a square matrix with a line of 1s running diagonal from upper-left to lower-right, with the rest of its entries as 0s.

### Matrix

Variables or constants arranged like a grid in rows and columns that together make up a rectangle. The**rows**go across, and the

**columns**are vertical; they're like the columns in the Lincoln Memorial. Here's a 2 × 2 matrix: