formula for a straight line

The formula for a straight line is:

`y = mx + c`

This is one of the most important basic maths formulas you must learn. 

To remember the formula for a straight line use the following mnemonic:

Why (`y`) have you made (m) egg (`x`) and (+) cress (`c`) sandwiches in a straight line?

Why (`y`) = made (m) egg (`x`) and (+) cress (`c`)

`y = mx + c`

Where m = gradient

and `c` = the point where the line crosses the `y` axis or goes through the `y` axis.

To remember that `c` is the point where the line goes through the `y` axis use the following mnemonic:

The sea lion (`c` line) jumped through the giant Y (`y` axis). 

Examples

1. Draw the following straight line on a graph

`y=2x+3`

First lets calculate some points on the graph.

If     `x=-2`               then   `y=2times(-2)+3=-1`

`x=-1`               then   `y=2times(-1)+3=1`

`x=0`                     then   `y=2times0+3\ \ \ \ \ \ \ \ =3`

`x=1`                     then   `y=2times1+3\ \ \ \ \ \ \ \ =5`

`x=2`                     then   `y=2times2+3\ \ \ \ \ \ \ \ =7`

Now draw a graph and plot the above points.

Now draw a straight line through these points

2. Draw the following straight line on a graph

`y=-2x+5`

First lets calculate some points on the graph.

If     `x=-2`               then   `y=-2times(-2)+5=9`

`x=-1`               then   `y=-2times(-1)+5=7`

`x=0`                     then   `y=-2times0+5\ \ \ \ \ \ \ \ =5`

`x=1`                     then   `y=-2times1+5\ \ \ \ \ \ \ \ =3`

`x=2`                     then   `y=-2times2+5\ \ \ \ \ \ \ \ =1`

Now draw a graph and mark out the above points.

Now draw a straight line through these points