# Defining a Coordinate System

## Overview

There are times when we need to read points on a coordinate plane.

## What is a coordinate plane?

A coordinate plane is two number lines that intersect. The first number line is called the **x-axis**. It travels horizontally. The second number line is called the **y-axis**. It travels vertically. The number lines intersect at the **origin**.

## How do you read a coordinate plane?

Each point on the plane is located with a set of coordinates called an ordered pair. The first number in the **ordered pair** tells you how far to travel across the **x-axis** from the origin. It’s called the **x**-coordinate. The second number tells you how far to travel up the **y-axis** from the **x**-coordinate. It’s called the y-coordinate.

Let’s give it a try.

Which ordered pair represents Point A on the coordinate plane below?

**(5, 2)****(2, 5)**

### Step 1: Locate Point A

All of the points are labeled. We can see that Point A is red in the coordinate plane.

### Step 2: Determine the x-coordinate

We know that the **x**-coordinate tells us how far to travel across the **x-axis** from the origin. So, we need to count how far Point A is from the origin.

### Step 3: Determine the y-coordinate

We know that the y-coordinate tells us how far to travel up the **y-axis** from the **x-axis**. So, we need to count how far Point A is from 2 on the **x-axis**.

### Step 4: Write the ordered pair

We know that the coordinates need to be presented in an ordered pair.

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Use the coordinate plane to answer this question.

Point A is on the __________.

- origin
- x-axis
- y-axis
- all of the above

y-axis

Point A is on the y-axis. Its coordinates are (0, 5).

Use the coordinate plane to answer this question.

Point B is on the __________.

- origin
- x-axis
- y-axis
- all of the above

x-axis

Point B is on the x-axis. Its coordinates are (4, 0).

Use the coordinate plane to answer this question.

Point C is on the __________.

- origin
- x-axis
- y-axis
- all of the above

all of the above

Point C represents the origin, but it is also where the x-axis and y-axis intersect. Therefore, it is on all three.

Use the coordinate plane to answer this question.

What is the y-coordinate of the Point A?

- 4
- 2
- 6

2

The point is up 2.

Use the coordinate plane to answer this question.

What is the x-coordinate of the Point A?

- 4
- 2
- 6

4

The point is over 4.

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