How to make 4 variable polynomial equatio

[afzal]

Can I use excel to make an equation for 4 variables (x,y,z,w)
e.g
a,b,c,d,3,f,g,h,i, would be constants

w = ax + by + cz + dx^2 + ey^2 + fz^2 + gxy + hyz + iyz

What are these equations called ?
What literature can I study to better understand the procedure of making these tye of equations.

I tried regression but the equation looks like

w = ax + by + cz + c

Is it possible on ay other software e.g MATLAB

 

[mfb]

What do you plan to do with the equation?
You can type this equation into excel (with cell references instead of variables). And now?

If you want to determine your constants in a fit, you can use the "solver" funktion, and use a cell which somehow determines the quality of your current constants to maximize/minimize/whatever this value.
Other programs might be better here.