: .
. . : . , () y = f(x1, x2,..., xn).
n (x1, x2,..., xn) n Rn. R2 , R3 -
. n y = f(x1, x2,..., xn), D Ì Rn Y Ì R, . D Y, (x1, x2,..., xn) Î D y Î Y.
D . (), Y . , z = f(x,y): (x.y) Î D Ì R2, z Î Z Ì R. x, y, z , z = f(x,y) .
.1 ,
D: 9 x2 y2 > 0, x2 + y2 < 32 - 3
Z: R = 3
f(x,y) = . . .1 x2 + y2 = .
u = f(x,y,z) . , , f(x,y,z) = .
.2 u = , D: x2 + y2 + z2 < 1 - R = 1 (0,0,0)
.
, , n.
z = f(x,y) D Ì R2 L, . D D. D , . . D , . . . (x,y), D, D . , . D . , , . (D), . d . d- .
.
. z = f(x,y) . (,) . 0(0,0) . , f(x,y) ... ̮0
lim [f(x.y) A] = 0 lim f(x,y) = A 0 (1)
( ).
|
|
M(x,y) d- 0 z e- . , d = d(e), 0 0 z A. , z A e > 0 d>0, :
|M0M| < d, |f(x,y) A| < e. (2)
. . , , , , ..
. z = f(x,y) . 0(0,0), 0 0:
lim f(x,y) = f(x0,y0) 0 (3)
. z = f(x,y) . E Ì D, .
. 0(0,0) . , . .
. z = xy / (x y). y = x - .
.
. z = f(x,y) .
Dz = f(x+Dx,y) f(x,y), y - Dyz = f(x,y+Dy) f(x,y).
. z = f(x,y) . Dz D :
z`x = z / x = lim Dz / Dx Dx 0 (4)
y: z`y = z / y = lim Dyz / D Dy 0
z`xdx z`ydy . . .
: z = f(x,y) y = const. y, , x = const.
. y = const z`x
, z = f(x,y) y = y0 ^ , z = f(x,y0). , z`x . z`y ^ (x = x0).
. z = f(x,y) . , .. z = f(x+ x, y+ y) f(x,y).
x y , .
. z = xy. z = y x, y z = x y, z = z + y z + x y
, y = f(x) , x: y = x + ( x). ,
dy = x = f (x) dx, ( x) x.