3. Limits
Definition :
If given any number ε >0
|f(x,y-L)| < ε
Whenever (x,y) lies in the domain of f and
0<√(x-x0)²+(y-y0)² < ∂
Then we say that limit of f9x,y0 is L as (x,y)
approaches (x0,y0) and we shall write
Lim f(x,y)= L
(x,y)->(0,0)
4. Continuity
The function u=f(x,y) is said to be continuity at
the pit (a,b), if for all points (x,y) near (a,b) the
value off9x,y) differs, but little , from the value
f(a,b).
In other wods, if f has the domain R and
Q=(a,b) is a point of R, then f is Continuous at
Q if for every ε>0 there exist a ∂ such that
|f(P)-f(Q)|=|f(x,y)-f(a,b)|< ∂…………
5. Continuity
………………For all P=(xy) in R for
which
PQ=√(x-a)²+(y-b)²< ∂
If a function is continuous at every
point of a domain R, w say that it is
continuous in R.
7. Partial derivatives of a function
Assuming that the function u=f(x,y) is defined
at the point (x0,y0), if we differentiate the
function u=F9xo,yo0 at the point x=x0 we btain
the partial derivative of f(x,y) with respect to x
at the point (x0,y0) :
Lim
h->0