Go Premium for a chance to win a PS4. Enter to Win

x
?
Solved

Excel: quadratic equation

Posted on 2011-09-27
15
Medium Priority
?
780 Views
Last Modified: 2012-05-12
Does excel have a quadratic equation function?
I have a set of points that I would like to fit ax^2+bx+c=0 though.
0
Comment
Question by:allelopath
  • 5
  • 4
  • 3
  • +2
15 Comments
 
LVL 12

Expert Comment

by:viralypatel
ID: 36709804
no direct function but this should solve the purpose:
http://www.bettersolutions.com/excel/EAV113/LT721811311.htm
0
 
LVL 27

Expert Comment

by:d-glitch
ID: 36710019
How many points do you have?  You need three points to determine a parabola.

If you have more than three points, you can use linear regression in Excel to solve for A, B, and C.
You have to set your data up in a table.  

For each data point:   x² is the coefficient of A     x is the coefficient of B      1 is the coefficient of C
0
 
LVL 1

Author Comment

by:allelopath
ID: 36710040
In this case, 105 points
0
What does it mean to be "Always On"?

Is your cloud always on? With an Always On cloud you won't have to worry about downtime for maintenance or software application code updates, ensuring that your bottom line isn't affected.

 
LVL 1

Author Comment

by:allelopath
ID: 36710062
like so
points.xls
0
 
LVL 27

Expert Comment

by:d-glitch
ID: 36710210
You have have a 105 values.  What do they mean?  What is x?

Why do you think this data should be fit to a quadratic?

These values are measurements of  ?????  varying with respect to ?????.
0
 
LVL 81

Accepted Solution

by:
byundt earned 2000 total points
ID: 36710299
Assuming that your x values are the numbers 1 through 106, then your quadratic formula might be:
y = -0.000514x2 + 0.048557x - 0.657532
R² = 0.695230


I array-entered the following formula in a 5 row x 3 column block of cells:
=LINEST(B2:B107,A2:A107^{1,2},TRUE,TRUE)
Among other things, it returns the coefficients a, b, c      for ax^2 + bx + c)

I also made a scatter plot
pointsQ27343514.xls
0
 
LVL 1

Author Comment

by:allelopath
ID: 36710336
d-glitch:
my apologies, the file I attached had only the y values. The x values should have been 0 - 105.
byundt, however, went the extra mile and figured it out.
0
 
LVL 81

Expert Comment

by:byundt
ID: 36710387
If x values are 0 to 105, then the R squared will be the same, but the coefficients will be slightly different:
y = -0.000514x2 + 0.047529x - 0.609489
R² = 0.695230


Brad
0
 
LVL 27

Expert Comment

by:d-glitch
ID: 36710392

Doing a rough fit by eye:

     Doing a rough fit by eye:

          -(60 - X)²                -X²      3X
    Y  =  ----------  +  0.5    =   ---  +  ----  -  8.5
            400                     400      10

Open in new window

0
 
LVL 37

Expert Comment

by:TommySzalapski
ID: 36710404
I seriously doubt that a quadratic is a good fit for your data. Should the data really start dropping rapidly with no lower bound as x gets higher?
0
 
LVL 37

Expert Comment

by:TommySzalapski
ID: 36710457
Here's a graph showing what the data of a best-fit quadratic would go compared to your data.
 best fit
0
 
LVL 27

Expert Comment

by:d-glitch
ID: 36710505
Needs some work, but it's a start.
ExEx-Quadratic.pdf
0
 
LVL 27

Expert Comment

by:d-glitch
ID: 36710531
TommySzalapski is way ahead here....
0
 
LVL 37

Expert Comment

by:TommySzalapski
ID: 36710681
I assumed byundt did a proper best-fit method to get his function and just used it. The point is that I am unsure that a quadratic is the right choice as d-glitch mentioned earlier. I repeat his questions here:
"These values are measurements of  ?????  varying with respect to ?????."
0
 
LVL 1

Author Comment

by:allelopath
ID: 36710803
TommySzalapski:
You have no way of knowing this, but project the data beyond 106 doesn't make sense.
The quadratic fits well enough to suit my purposes.
0

Featured Post

Industry Leaders: We Want Your Opinion!

We value your feedback.

Take our survey and automatically be enter to win anyone of the following:
Yeti Cooler, Amazon eGift Card, and Movie eGift Card!

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

This article describes a serious pitfall that can happen when deleting shapes using VBA.
Windows Explorer let you handle zip folders nearly as any other folder: Copy, move, change, and delete, etc. In VBA you can also handle normal files and folders, but zip folders takes a little more - and that you'll find here.
This Micro Tutorial demonstrate the bugs in Microsoft Excel for Mac with Pivot Charts.
This is a video describing the growing solar energy use in Utah. This is a topic that greatly interests me and so I decided to produce a video about it.

971 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question