Is there a software that can find critical points for x,y,z coordinates?

This is for Numerical Analysis. The professor wants us to get more involved with using softwares instead of relying on hand by hand. So he intentionally gives us questions that are impossible to solve by hand. I have a function of f(x,y,z), set up a gradient, and put everything into macro on excel. I just need a reliable software to help find a critical point. 

2020-04-25T04:02:20Z

Let me rephrase that.

I have a function of f(x,y,z). I already set up a gradient and put everything on excel in the form of macro.

2020-04-25T04:02:41Z

The online calculator I found is only good for x and y.

2017-04-11T00:37:33.809Z