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
y-INTERCEPT | The point on the y-axis where the line crosses through. |
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).