How can i find an X value given a Y value?

J

jmi

I can use the "forecast" formula to find a Y value given an X, but not the
other way around. please help! thanks
 
D

David Biddulph

Can't you just reverse the order in which you give the second and third
arguments of the FORECAST() function?
In other words, instead of =FORECAST(x,known_y's,known_x's), use
=FORECAST(y,known_x's,known_y's) ?
 
M

Mike Middleton

jmi -

Behind the scenes, FORECAST uses the least-squares method for fitting a
simple linear function.

So, instead of using FORECAST, use the SLOPE and INTERCEPT worksheet
functions.

Since Y = Intercept + Slope*X, a little algebra indicates X = (Y -
Intercept)/Slope.

- Mike
http://www.mikemiddleton.com
 
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