Regression model does not provide correct quadratic equation
Hello:I created a 2^3 full factorial experiment with 4 center points. X1, X2 and X3 are the factors and Y is the response. X2 and X3 are just any random factor, but X1 is the radius and Y is the area. So mathematically relation is Y=3.14*X1^2Below are the three scenarios where I computed regression equation based on just X1, both X1 and X1^2 and only X1^2. When I only consider X1^2, it is no more...