Mammoth Memory

Formula for a straight line

The formula for a straight line is:

 `y=mx+c`

 The formula of straight line graphs is y=mx+c where m is the gradient and c is the point where the line crosses the y axis 

 Where `m=` Gradient

                `c=` The point where the line crosses the `y` axis (`y` intercept)

 


 

Further explanation

Equations of a straight line are in the form of:

`y=mx+c`

 

If you are given a formula of a straight line and asked to draw it on a graph you do so as follows:

 

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.

Example 1 drawing the graph and plotting the points

Now draw a straight line through these points

Example 1 straight line connecting the points that have been plotted on the straight line graph 

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.

Example 2 drawing the graph and plotting the points 

Now draw a straight line through these points

Example 2 straight line connecting the points that have been plotted on the straight line graph 

 

 

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