> >
>

# Anyone good with Excel?!?!?!?

Foo Off-Topic chit chat with no general subject.

# Anyone good with Excel?!?!?!?

05-05-09, 06:05 PM
#1
Jynx
.....

Join Date: Aug 2006
Location: Long Island
Posts: 4,816

Bikes: 2006 Cannondale CAAD8

Mentioned: 0 Post(s)
Quoted: 3 Post(s)
Anyone good with Excel?!?!?!?

Hey guys I am looking for some help with excel. I will explain what I am doing...

I have an XY scatter plot for three different sets of data. I am adding a best fit line (trendline) for each set. Best fit is a polynomial order of 2. Everything is okay except it is giving me the equations as

y = 3E-05x^2 - 0.0004x

and

y = 3E-05x^2 - 0.0005x

I want to force out the linear part and just have it as

y = cx^2

How can I go about doing this? Thanks!
__________________
Weight Listing Index (Feel Free to add to it!)

Last edited by Jynx; 05-05-09 at 06:10 PM.

05-05-09, 08:19 PM
#2
byte_speed

Join Date: Sep 2004
Location: East Tennessee
Posts: 858

Bikes: 2002 Lightspeed Classic; 2010 Pedalforce RS

Mentioned: 0 Post(s)
Quoted: 0 Post(s)
I think you are missing something, this is an algebra problem, not Excel
(but you could use Excel to solve for x)

Since both equations = y; then:

3E-05x^2 - 0.0004x = 3E-05x^2 - 0.0005x

then subtract 3E-05x^2 from both sides to get:

- 0.0004x = - 0.0005x

The only value of x where that works is x = 0

I would need to see the original data to fit a y = cx^2 type curve,
which I would be happy to do, but it may be a day or two before I can get to it.

05-05-09, 08:29 PM
#3
valygrl
Senior Member

Join Date: Jul 2003
Location: Boulder, CO
Posts: 8,546
Mentioned: 83 Post(s)
Quoted: 163 Post(s)
Right-click on the trendline, select "Format Trendline" select Options, select a linear trendline instead of polynomial.

edit, sorry that's Type, not Options

05-06-09, 05:12 AM
#4
Jynx
.....

Join Date: Aug 2006
Location: Long Island
Posts: 4,816

Bikes: 2006 Cannondale CAAD8

Mentioned: 0 Post(s)
Quoted: 3 Post(s)
Originally Posted by byte_speed
I think you are missing something, this is an algebra problem, not Excel
(but you could use Excel to solve for x)

Since both equations = y; then:

3E-05x^2 - 0.0004x = 3E-05x^2 - 0.0005x

then subtract 3E-05x^2 from both sides to get:

- 0.0004x = - 0.0005x

The only value of x where that works is x = 0

I would need to see the original data to fit a y = cx^2 type curve,
which I would be happy to do, but it may be a day or two before I can get to it.

It is in excel. The two formulas are for two different sets of data so they are not equal.

Originally Posted by valygrl
Right-click on the trendline, select "Format Trendline" select Options, select a linear trendline instead of polynomial.

edit, sorry that's Type, not Options
Unfortunately I need to do a polynomial best fit. The data I am graphing is force of drag versus wind velocity. I can not get an accurate best fit with a linear trendline.
__________________
Weight Listing Index (Feel Free to add to it!)

05-06-09, 07:12 AM
#5
valygrl
Senior Member

Join Date: Jul 2003
Location: Boulder, CO
Posts: 8,546
Mentioned: 83 Post(s)
Quoted: 163 Post(s)
Originally Posted by Jynx
It is in excel. The two formulas are for two different sets of data so they are not equal.

Unfortunately I need to do a polynomial best fit. The data I am graphing is force of drag versus wind velocity. I can not get an accurate best fit with a linear trendline.
Ok, it's been a long time and I don't remember the terminology well..

but I think a polynomial equation is
y = ax^2 + bx + c

and if you try to get rid of the "bx" + c part you're just going to have a parabola.

but if you want it to force that, you have to create a separate data range that contains data that expresseses the equation you want to graph, and graph it. - I found this by googling "graph equation in excel" http://peltiertech.com/Excel/ChartsH...tEquation.html

05-06-09, 10:14 AM
#6
Jynx
.....

Join Date: Aug 2006
Location: Long Island
Posts: 4,816

Bikes: 2006 Cannondale CAAD8

Mentioned: 0 Post(s)
Quoted: 3 Post(s)
Originally Posted by valygrl
Ok, it's been a long time and I don't remember the terminology well..

but I think a polynomial equation is
y = ax^2 + bx + c

and if you try to get rid of the "bx" + c part you're just going to have a parabola.

but if you want it to force that, you have to create a separate data range that contains data that expresseses the equation you want to graph, and graph it. - I found this by googling "graph equation in excel" http://peltiertech.com/Excel/ChartsH...tEquation.html
Thank you. I figured it out.
__________________
Weight Listing Index (Feel Free to add to it!)

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off