curve fit for multi variables equation

[#1]

I have some results, I want to use curve fit to find the equation which can describe the relation between the variables.I have three(3) variables so the equation should has this format " y=f( x1, x2, x3 ) " . I would be appreciate if you lead me how can I use curve fit to find an equation with three variables?

[#2]

Adel,  I would start with the "Fit Model" platform and discover the best equation for y=f(X1, X2, X3).  Then, it will be a pretty easy exercise to plot your data on a 3-D graph.

[#3]

Adel,

Have you fit the model and then saved the prediction formula?  If so, you can go to your data table and right click on the column header for the prediction formula and then select "Formula" from the list.  This will show the formula in the format you suggest above, keeping in mind that Y is implied.  If you want to see how predictive your model is go to the Fit YbyX platform and then put the original Y data in Y Response and the saved prediction formula in X Factor and click OK.  You can then go to the red hot spot by Bivariate fit and select Fit Line to get fit statistics.