Question: what is the linearization formula?
Answer: The Linearization of a function f(x,y) at (a,b) is L(x,y) = f(a,b)+(x−a)fx(a,b)+(y−b)fy(a,b). This is very similar to the familiar formula L(x)=f(a)+f′(a)(x−a) functions of one variable, only with an extra term for the second variable.