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November 21st, 2015, 11:08 AM   #1
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Question Graphs.... Can anyone help ?

How can I draw a graph using a scale of 2cm to 1 unit on the x-axis and 1 cm to 1 unit on the y-axis?

y = 1/2x + 4
-3 < x < 3

Last edited by skipjack; November 21st, 2015 at 12:50 PM.
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November 21st, 2015, 12:05 PM   #2
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1. Get a sheet of paper!
2. Draw a horizontal line and a vertical line crossing at the center of the paper.
3. On either side of the vertical line, mark points on the horizontal line at distance 2 cm, 4 cm, and 6 cm from the vertical line. Since 2 cm corresponds to 1 unit, those points will correspond to x values of 1, 2, and 3 on the graph to the right of the vertical line, and x values of -1, -2, and -3 on the graph to the left of the vertical line.
4. On either side of the horizontal line, mark points on the vertical line at distance 1cm, 2 cm, 3 cm, 4 cm, 5 cm, and 6 cm above and below the horizontal line. Since 1 cm corresponds to 1 unit, these will correspond to y values of 1, 2, 3, 4, 5, and 6 above the horizontal line and -1, -2, -3, -4, -5, and -6 below the horizontal line.

That's the hard part- setting up the graph structure. Now the easy part: Since y= (1/2)x+ 4 is a "linear" function, its graph is a straight line and a straight line is determined by two points. If x= 3, then y= (1/2)(3)+ 4= 3/2+ 8/2= 11/2= 5 and a half. The point (3, 11/2) is directly above the x= 3 mark at a height half way between the y= 5 and y= 6 marks on the vertical axis. Mark that point. If x= -3, then y= (1/2)(-3)+ 4= -3/2+ 8/2= 5/2= 2 and a half. The point (-3, 5/2) is directly above the x= -3 mark halfway between the y= 2 and y= 3 marks on the vertical axis. Mark that point. Finally, draw the straight line segment between those two points.

Last edited by skipjack; November 21st, 2015 at 12:35 PM.
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November 21st, 2015, 12:31 PM   #3
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Click below to enlarge, then spot the missing detail...

LinePlot.PNG
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November 23rd, 2015, 03:15 AM   #4
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Quote:
Originally Posted by Country Boy View Post
1. Get a sheet of paper!
2. Draw a horizontal line and a vertical line crossing at the center of the paper.
3. On either side of the vertical line, mark points on the horizontal line at distance 2 cm, 4 cm, and 6 cm from the vertical line. Since 2 cm corresponds to 1 unit, those points will correspond to x values of 1, 2, and 3 on the graph to the right of the vertical line, and x values of -1, -2, and -3 on the graph to the left of the vertical line.
4. On either side of the horizontal line, mark points on the vertical line at distance 1cm, 2 cm, 3 cm, 4 cm, 5 cm, and 6 cm above and below the horizontal line. Since 1 cm corresponds to 1 unit, these will correspond to y values of 1, 2, 3, 4, 5, and 6 above the horizontal line and -1, -2, -3, -4, -5, and -6 below the horizontal line.

That's the hard part- setting up the graph structure. Now the easy part: Since y= (1/2)x+ 4 is a "linear" function, its graph is a straight line and a straight line is determined by two points. If x= 3, then y= (1/2)(3)+ 4= 3/2+ 8/2= 11/2= 5 and a half. The point (3, 11/2) is directly above the x= 3 mark at a height half way between the y= 5 and y= 6 marks on the vertical axis. Mark that point. If x= -3, then y= (1/2)(-3)+ 4= -3/2+ 8/2= 5/2= 2 and a half. The point (-3, 5/2) is directly above the x= -3 mark halfway between the y= 2 and y= 3 marks on the vertical axis. Mark that point. Finally, draw the straight line segment between those two points.


Thanks for help,

Last edited by Hams; November 23rd, 2015 at 03:21 AM. Reason: The graph paper that i will draw on is the one that contains very small squares right ?
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November 23rd, 2015, 03:16 AM   #5
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Quote:
Originally Posted by skipjack View Post
Click below to enlarge, then spot the missing detail...

Attachment 7014
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November 24th, 2015, 03:36 PM   #6
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Quote:
Originally Posted by Hams View Post
How can I draw a graph using a scale of 2cm to 1 unit on the x-axis and 1 cm to 1 unit on the y-axis?

y = 1/2x + 4
-3 < x < 3
I don't like when a teacher or professor instructs a student to make a graph that uses different scales when working with small numbers (obviously if you have to graph y = 100x+2 you would want different scales or the line would be so steep it would look vertical). I remember when a student was instructed to graph that way during the 1998-1999 school year. When I told her that her graph wasn't to scale, she said her teacher wanted it that way.
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