How to prove the continuity of the two-dollar function can ...

This refers to the proof of a point in a region.

1. Continuity

Use the limit to do

if (x, y) tends to (x0,y0) s The limit of f (x, Y) is F (x0,y0) then the function is continuous

2 bias conductivity

If f (x, y) is equal to the bias of X and the bias of Y to (x, y) equals (x0,y0), then the function can be biased

3 Micro-Usability

First assume the function is micro, dz=f (x0,y0) dx+f (x0,y0) dy+w

Then, according to Dz=f (X0+dx,y0+dy)-F (x0,y0), the solution of W

If W is the higher order infinity of the Radical (x^2+y^2), then the function can be slightly

Above