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# Excel graph for solving simultaneous equations

Posted on 2011-03-25
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Need someones help to develop a graph which plots two lines for solving a simultaneous equation. Manually when the graph is plotted with when x=0 and y= a value and when x= a value and y=0 for both sets of equations.

Sample data is as below:

Eqn (1):           -1x - 12y = 54
when x=0, y=-4.5 and when y=0, x= -54

Eqn (2):         4x + 3y = 25
when x=0, y=8.3333 and when y=0, x=6.25

When the two lines are plotted for the above equatons, where they cross I will need the x and y value which is the solution for the simultaneous equation.

I don't mind whether the solution uses vba or not.
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Question by:Baber62
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LVL 28

Expert Comment

This sounds like homework, and you should probably try to do it without posting it here, since that defeats the purpose.

That said, Excel can't plot equations, since it's not a TI calculator. The closest you can get is to do a line graph with a few sample points - since these are linear equations, that shouldn't be too difficult to give it a few example pairs and have it graph them for you.

It won't calculate the intersection though - it's not really designed to do that, so you'll have to do it by hand using substitution.
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Author Comment

Thanks for the tip Ryan, but I am a part time teacher and need this to demonstrate to students. I have attached a workbook I have developed to solve simultaneous equations, all my own work.

That's the difficulty I am having at the moment is trying to understand how to get two lines to plot on one graph from separate datasets.
Simultaneous-Equations.xlsx
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LVL 7

Expert Comment

you would have to solve each equation multiple times and list the x,y data points.  Then you could plot a graph with both series.  But its still not going to tell you where they intersect, you would have to eyeball that...or solve for it.

Travis
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Accepted Solution

harr22 earned 167 total points
here is a little example using your equations

Simultaneous-Equations.xlsx
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LVL 43

Assisted Solution

Saqib Husain, Syed earned 166 total points
To be able to plot the two lines from the four selected points you should move the two points of one line away from the two points of the other so that there is at least one blank space between the data. Then select the data and (Assuming that you are using excel 2007 or later)

Insert tab > Scatter > select one of the last two types.

This will plot the two lines for you.

The problem in this particular example is that the intersection point does not lie on any of the two line segments plotted. They will both have to be extended so that the intersection point is evident

I have modified your range as explained above and plotted a chart in the attached file.

I have also created a similar range and included the intersection point in it and then plotted it to show the intersection point.

Saqib
Copy-of-Simultaneous-Equations.xlsx
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LVL 26

Expert Comment

Baber62,

Must this be an Excel solution? If not, have you considered the (free) (Microsoft Mathematics 4.0? This seems to do everything you want "out of the box".

Regards,
Brian.
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Assisted Solution

redmondb earned 167 total points
Baber62,

For example...

(1) Click on "Equation Solver" on the Ribbon.
(2) Select "Solve a System of 2 Equations".
(3) Enter the two equations and click on "Solve"...
(4) Clicking on "Solution Steps Using Elimination"...

Regards,
Brian.
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Author Closing Comment

Thanks guys and gals for your help. It is sincerly appreciated.
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LVL 26

Expert Comment

Thanks, Baber62.
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