Graphing Direct Variation

Date: 02/27/2003 at 15:06:24
From: Jennifer
Subject: How do you graph direct variation

How do you graph direct variation?  I thought you had to have two 
coordinates to graph a line.  How do you do it with the formula 
y = mx+b?

Example: y = 2x-3

Thanks for your help.
Jennifer

Date: 02/27/2003 at 17:59:53
From: Doctor Douglas
Subject: Re: How do you graph direct variation

Hi, Jennifer!

Direct variation between x and y means that the relationship between
them is of the form

   y = k*x

where k is some constant.  This means that the origin (0,0) is a point 
on this line, and so it only takes one additional point (x0,y0) to 
specify the line:

  y = k*x = (y0/x0)*x

So it IS of the form y = mx+b, except that b must be zero in the 
case of direct variation.

Does that help?  Write back if you still have questions about this.

- Doctor Douglas, The Math Forum
  http://mathforum.org/dr.math/