. .
(,) - z, . z=f(x,y,)
z - (,), z .
( ) , .
- P, z=f(x,y)
M0 (0;y0) r (x,y), < r
. .
.
, . f (x, y) ( 0, 0), , :
(1)
( f (x, y) → (x, y) → ( 0, 0)), ( 0, 0), , ,
(2)
( 0, 0) (xk,yk).
, , : f ( 0, 0) , , ( 0, 0) , , , ε > 0 δ > 0,
| f (x, y) A | < ε (3)
(x, y),
0 < < δ. (4)
, , : ε > 0 δ- ( 0, 0) , (x, y) , ( 0, 0), (3).
(x, y) ( 0, 0) = 0 + Δ , = 0 + Δ , (1) :
, ( 0, 0), , , .
ω = (ω , ω ) (|ω|2 = ω 2 + ω 2 = 1) t > 0 .
( 0 + t ω , y 0 + t ω ) (0 < t)
, ( 0, 0) ω. ω
f ( 0 + t ω , y 0 + t ω ) (0 < t < δ)
t, δ .
( t)
f ( 0 + t ω , y 0 + t ω ),
|
|
, f ( 0, 0) ω.
1.
(x, y) 0 = 0, 0 = 0. (, ):
( ε > 0 δ = ε/2 | f (x, y) | < ε, < δ).
, , k , y = kx
, φ (0, 0) ( y = kx, > 0,
).
f(M) → 0, ε > 0 δ > 0, , 0 | 0 | < δ, | f(M) | < ε.
. f 1 (M) f 2 (M) → 0 , :
)
)
)
f (x, y) ( 0, 0), , ( 0, 0) f (x, y) :
(1)
f ( 0, 0) :
(1")
.. f ( 0, 0), f ( 0+ Δ , 0 + Δ ) Δ , Δ Δ = Δ = 0.
Δ = f (x, y) (x, y), Δ , Δ
Δ = f ( + Δ , + Δ ) f (x, y)
f (x, y): f (x, y),
(1"")
. , , ( 0, 0) f φ , , , φ ( 0, 0) ≠ 0.
f (x, y) = x,y. ,
| f (x, y) f ( 0, 0) | = | | = 0 0.
f (x, y) = f (x, y) = . (x, y), . , f (x, y) = (x, y) , . (x, y) :
| f ( + Δ , + Δ ) f (x, y) | = | f ( + Δ ) | = | Δ | ≤ 0.
x, y , , , x, y. x, y (x, y) R 2.
P/Q (x, y) (x,y), , R 2, (x, y), Q(x, y) = 0.
(x, y) = 3 2 + 2 4
(x, y) ,
(x, y) = 4 2 2 2 + 4
(x, y) .
, .
|
|
. f (x, y, z) (x 0, y 0, z 0 ) R 3 ( (x, y, z)),
x = φ (u, v), y = ψ (u, v), z = χ (u, v)
(u 0, v 0 ) R 2 ( (u, v)). , ,
x 0 = φ (u 0, v 0 ), y 0= ψ (u 0, v 0 ), z 0= χ (u 0, v 0 ).
F (u, v) = f [ φ (u, v), ψ (u, v), χ (u, v) ] (
(u, v)) (u 0, v 0 ).
. ,
. f (x, y), ( 0, 0) , f ( 0, 0) ( 0, 0).
f (x) = f (x 1,..., ) 0 = ( 01,..., 0 ), , 0, 0 :
(2)
f 0 :
(2")
.. f (x) 0, f ( 0 + h) h h = 0.
f 0, h = (h 1,..., h),
Δ h f ( 0 ) = f ( 0 + h) f ( 0 )
f 0: f 0,
(2"")
. , , 0 f (x) φ (x) , , , φ ( 0 ) ≠ 0.
. Δ h f ( 0 ) f 0.
Rn = (x 1,..., ) G.
0 = ( 01,..., 0 ) G, , G.
G Rn , .
,
1 = φ1 (t),..., = φ (t) (a ≤ t ≤ b)
[ a, b ], Rn, 1 = ( 11,..., 1 ) 2 = ( 21,..., 2 ), 11 = φ1 (),..., 1 = φ (), 21 = φ1 (b),..., 2 = φ (b). t .
G , 1, 2 , G.
.
. f (x) Rn ( Rn). G ,
f (x) > ( f (x) < ), , .
, F(x) = f(x) Rn, , F(x) > 0, G. 0 G,
| 0 | < δ,
F(x) > 0, .. G 0 G G.
f (x) < .
, f () 0, :
) f () 0 ;
) ;
)
0 , . , . . f () G, .
1. : z = ln (x 2 + y 2 ).
. z = ln (x 2 + y 2 ) = 0, = 0. , (0, 0) .