You are correct davesexcel:

This quadratic has two separate solutions:
one around .0576 and the other around 31.82548752

=(-2.8089+(2.8089^2-4*(-0.0881)*(-0.1615))^0.5)/(2*(-0.0881))
=(-2.8089- (2.8089^2-4*(-0.0881)*(-0.1615))^0.5)/(2*(-0.0881))

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Gary's Student


"davesexcel" wrote:


0.057672821
y= -0.0881x^2+2.8089x+0.0505.

If the absorbance reading (y) = 0.212, how do I calculate the value of
x?
I am just thinking
A1=B2
B2=-.0881*C1^2+2.8089*C1+.0505
then I went to Tools, Goal seek
set the value of A1 to .212 by changing Cell C1


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davesexcel
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