Converting Polynomial equation

jmenche

New Member
Joined
Jun 2, 2006
Messages
26
Hi,

I fit a polynomial line to a chart and got the following equation: -5E+06x^2 + 7E+07x + 1E+08

How do I use this as a formula in a cell?

Thanks
Jeff
 

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jmenche

New Member
Joined
Jun 2, 2006
Messages
26
I actually need help fixing a forecast of mine (or explaining) but just realized that you cannot attach a file.

Can I email someone a file?
 

shg

MrExcel MVP
Joined
May 7, 2008
Messages
21,746
Office Version
2010
Platform
Windows
You could put a workbook on dropbox or box.net and post a link.

Using the coefficients from a trendline formula on a graph is a bad idea -- there is insufficient precision shown by default, and if you fix that by formatting, it is an error-prone, manual mess to copy the coefficients.

The alternative is to use LINEST to get the coefficients on the worksheet, which is easy, but forecasting with a polynomial is a bad idea -- they will fit anything, but the fit doesn't have much meaning. A linear (constant change YoY) or exponential (constant mutiple YoY) trendline makes more sense. You can also get those coefficients with LINEST.
 

shg

MrExcel MVP
Joined
May 7, 2008
Messages
21,746
Office Version
2010
Platform
Windows
B​
C​
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H​
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nPds
4​
26​
5​
Period
"Month"
Sales
Centered Moving Average
2. Deseas Sales
"Month"
Average
1. Seasonal Index
Period
"Month"
Deseas Forecast
4. Seasonalized Forecast
6​
1​
1​
203,005,432​
268,417,835​
1​
0.756​
0.756​
27​
296,631,702​
224,343,686.35​
7​
2​
2​
226,512,619​
269,786,418​
2​
0.840​
0.840​
28​
297,772,764​
250,009,948.34​
8​
3​
3​
256,928,553​
270,973,922​
3​
0.948​
0.948​
29​
298,918,215​
283,424,411.86​
9​
4​
4​
273,629,408​
272,008,999​
4​
1.006​
1.006​
30​
300,068,073​
301,855,634.94​
10​
5​
5​
313,696,609​
272,901,824​
5​
1.149​
1.149​
31​
301,222,354​
346,250,639.64​
11​
6​
6​
370,954,905​
273,651,321​
6​
1.355​
1.356​
32​
302,381,075​
409,900,243.99​
12​
7​
7​
386,627,902​
1.409​
274,321,813​
7​
1.409​
1.409​
33​
303,544,254​
427,813,875.77​
13​
8​
8​
355,867,698​
1.293​
275,143,614​
8​
1.293​
1.293​
34​
304,711,907​
394,110,999.26​
14​
9​
9​
308,782,450​
1.118​
276,060,576​
9​
1.118​
1.119​
35​
305,884,051​
342,140,946.72​
15​
10​
10​
269,147,199​
0.971​
277,100,667​
10​
0.971​
0.971​
36​
307,060,705​
298,247,310.52​
16​
11​
11​
232,158,090​
0.834​
278,208,366​
11​
0.834​
0.834​
37​
308,241,884​
257,220,328.41​
17​
12​
12​
194,888,882​
0.697​
279,478,264​
12​
0.697​
0.697​
38​
309,427,608​
215,773,490.71​
18​
13​
13​
174,345,766​
0.620​
280,979,953​
13​
0.620​
0.620​
39​
310,617,892​
192,735,865.20​
19​
14​
1​
213,689,928​
0.756​
282,545,090​
Totals
13
13.000
40​
311,812,756​
235,825,175.51​
20​
15​
2​
238,434,335​
0.840​
283,985,703​
41​
313,012,215​
262,804,988.65​
21​
16​
3​
270,451,109​
0.948​
285,235,708​
LOGEST Regression
m
1.0038​
42​
314,216,289​
297,929,541.76​
22​
17​
4​
288,030,955​
1.006​
286,325,262​
b
267,422,242​
43​
315,424,994​
317,304,040.27​
23​
18​
5​
330,206,957​
1.149​
287,265,078​
44​
316,638,349​
363,971,098.05​
24​
19​
6​
390,478,847​
1.355​
288,054,022​
3. Monthly Growth Rate
0.38%​
45​
317,856,372​
430,878,169.80​
25​
20​
7​
406,976,739​
1.409​
288,759,803​
46​
319,079,079​
449,708,587.66​
26​
21​
8​
374,597,576​
289,624,857​
47​
320,306,491​
414,280,861.13​
27​
22​
9​
325,034,158​
290,590,080​
48​
321,538,623​
359,651,078.75​
28​
23​
10​
283,312,841​
291,684,913​
49​
322,775,496​
313,511,048.57​
29​
24​
11​
244,376,937​
292,850,912​
50​
324,017,126​
270,384,382.45​
30​
25​
12​
205,146,192​
294,187,646​
51​
325,263,533​
226,816,373.32​
31​
26​
13​
183,521,859​
295,768,372​
52​
326,514,734​
202,599,725.35​

See the last tab of the workbook at https://app.box.com/shared/5gi9g8x23p
 

shg

MrExcel MVP
Joined
May 7, 2008
Messages
21,746
Office Version
2010
Platform
Windows
You're welcome.
 

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