To find the y-intercept, calculate 
and 
, the average of the x- and y-values, respectively.
Then substitute these two values for x and y in the
= b + a equation. Finally, solve for the unknown quantity a. Remember from the previous page that:
b = 0.002 = slope
0.35 = a + 0.002(175)
0.35 = a + 0.35
0 = a
Therefore, the complete relationship between glucose concentration and absorbance for the data is
y = 0+ 0.002
x, or
y = 0.002
x, where
y is the absorbance and
x is the glucose concentration.
