Mathematica question

1. The problem statement, all variables and given/known data
I draw two 3D graphs in Mathematica by using the "Plot3D "and I want to Show the difference between these two graphs. Can anyone tell me what command should I use?

2. Relevant equations


3. The attempt at a solution

 

Thank you so much, this is something I needed. and I defined a new function which is difference of my two first function, like this (( a:= my first function and b:=my second function & c=a-b )) . I hope it works now.