(Taylor series in two variables is
optional material -- check with your instructor to see if you
need this.)
Partial derivatives allow us to approximate functions just like
ordinary derivatives do, only with a contribution from each
variable. If x≈a and y≈b, then we can get a
two-variable linear approximation
that is analogous to the linear approximation L(x) in one
variable f(x,y)≈f(a,b)+fx(a,b)(x−a)+fy(a,b)(y−b).
This is sometimes written as df=∂f∂xdx+∂f∂ydy.
And, just as in one dimension, we can use higher derivatives to
get a more accurate approximation.
Taylor
Series in two variables:f(x,y)=∞∑n,m=0cn,m(x−a)n(y−b)m,
where
cn,m=1n!m!∂n+mf∂xn∂ym(a,b).
This video explores the Taylor Series in two variables and looks
at an example.