May 5th, 2010, 04:30 AM  #1 
Senior Member Joined: Mar 2010 From: Melbourne Posts: 178 Thanks: 0  Plotting
Hi, I have two functions: y = 1/5 (4x 3) and its inverse function: y = 5x+3/4  How do I plot and represent these on an xy graph ? wulfgarpro. 
May 5th, 2010, 05:28 AM  #2 
Global Moderator Joined: Nov 2009 From: Northwest Arkansas Posts: 2,766 Thanks: 4  Re: Plotting
I prefer to start with the equations in "slopeintercept form" (i.e. "y = mx + b"). Consider the equation y = (3/4)x + (5) The slope is 3/4. This means that a vertical increase of 3 units corresponds to a horizontal increase of 4 units. ("rise over run") The yintercept is (5). You can find this directly by evaluating when x = 0... Step 1: Plot the yintercept. In this case, we go down 5 units from the origin and mark the point (0, 5). Step 2: Use the SLOPE to get from this point to another point, and then from your new point to another, and so on. So from (0,5), we go UP 3 and RIGHT 4 units. Up 3 to (0,2) and right 4 to (4,2) (4, 2) is another point on the line. At this point you can draw the line containing the two points and you're done. Another method is to use the intercepts. Let's look at your "inverse" equation y = 5x + 3/4 When x = 0, y = 3/4 When y = 0, 5x = 3/4, so x = 3/20. This information can be consolidated to the two points: (0,3/4) and (3/20, 0). Plot these points. Draw the line containing them. Boom. 

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