# Straight line graphs

## In a nutshell

Straight lines join two points on a coordinate grid and continue past those points infinitely. There are two types of basic straight line graphs: horizontal, and vertical, each recognisable from their equation.

**Definitions**

**$\bf{y}$-INTERCEPT** | The point on the $y$-axis where the line crosses through. |

$\bf{x}$**-INTERCEPT** | The point on the $x$-axis where the line crosses through. |

**HORIZONTAL ** | A straight line going left to right. Think of the "horizon" to help you remember. |

**VERTICAL** | A straight line going up and down. |

## Equations of the basic straight line graphs

The equation of a horizontal line is

$y=c$

where $c$ is the $y$-intercept. A vertical line has equation

$x=d$

where $d$ is the $x$-intercept.

## Using the equation to draw a basic straight line

To draw either a horizontal or a vertical line using its equation follow this procedure:

#### procedure

**1.**
| Decide whether the equation is for a horizontal line ($y=c$) or a vertical line ($x=d$). |

**2a.**
| If horizontal, draw a horizontal line that passes through the point $(0,c)$. |

**2b.**
| If vertical, draw a vertical line that passes through the point $(d,0)$. |

**Note:*** Every point on a horizontal line has the same $y$-coordinate and every point on a vertical line has the same $x$-coordinate.*

##### Example

*Draw the lines $y=5$ and $x=-3$.*

*The line $y=5$ is horizontal and passes through the point $(0,5)$. The line $x=-3$ is vertical and passes through $(-3,0)$.*