plotting 3d graphs on c#

I wanted to know how I get a picture or plot of a 3d function that you input on c#. Is there any free software for this?

like for example plotting f1 below:
double f1 = Math.Pow(x*y,2); return f1;

Help would be much appreciated. I am new to c# and coding altogether!

We are using FastGraph Library for 3D display routines.
That is not free but that is good and easy to use . They have supported many programming languages.