Regression for Nonlinear Data the Quadratic Fitting Function

6 Regression for Nonlinear Data the Quadratic Fitting Function 

Fortunately, in most cases of interest in this book the deviations of the raw data from hneaiity are not very large even with extensive ranges for Xj and Yj and can usually be handled by using a simple quadratic relationship instead of Equation [8.19a]  

In the general case for the fitting function given as Equation [8.53], the following equations apply (Schwartz 1977)  

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