# Coordinates in the Plane

To represent points in the plane, two perpendicular straight lines are used. They are called the **Cartesian axes** or **coordinate axes**.

The **horizontal axis** is called the **x-axis**.

The **vertical axis** is called the **y-axis**.

Point **O**, where the two axes intersect is called the **origin**.

The coordinates of a point, **P**, are represented by **(x, y)**.

The **distance** measured along the **horizontal axis** is the **x-coordinate** or the **abscissa**.

The **distance** measured along the **vertical axis** is the** y-coordinate** or the **ordinate**.

## Plotting Points

The **coordinate axes** divide the plane into four equal parts called **quadrants**.

### Signs

Quadrant | Abscissa | Ordinate |
---|---|---|

I | + | + |

II | − | + |

III | − | − |

IV | + | − |

The **origin**, **O**, has coordinates **(0,0)**.

The points that are on the **vertical axis** have their **abscissa** equal to **0**.

The points that are on the **horizontal axis** have their **ordinate** equal to **0**.

The points in the **same horizontal line** (parallel to the x-axis) have the **same ordinate**.

The points in the **same vertical line** (parallel to the y-axis) have the **same abscissa**.

#### Exercise

Plot the following points:

A(1, 4), B(-3, 2), C(0, 5), D(-4, -4), E(-5, 0), F(4, -3), G(4, 0), H(0, -2)