Can I obtain x values from y values on an Excel chart?

[Helen]

I've constructed an exponential curve, is there a function whereby I can
enter new y values to obtain the corresponding x values, instead of having to
print it off and read off manually?

Many thanks from a novice

-Helen Moore

 

[Bernard Liengme]

if Y=A*Exp(BX); then Ln(Y) - Ln(A) = BX or X= (Ln(Y) -Ln(A))/B

Also remember you can use LOGEST or LINEST to extract the trendline
coefficients into cells rather than copying them form equation on chart; see
http://www.stfx.ca/people/bliengme/ExcelTips/ExponentialTrendline& LOGEST.htm
http://www.stfx.ca/people/bliengme/ExcelTips/Polynomial.htm
best wishes