. S = xy. , S . ( , j ) .
D z, , z , D. : z = f(x, y), j(x, y) ..
D , z = f(x, y) . , , ( (), () ). z = f(x, y) . ( , :
z = py + qx + t, (. (1.54)).
( ). , , .
z=f(x,y) u=f(x,y,z) . z=f(x,y) f(x,y) = , . : , , ..
u=f(x,y,z) f(x,y,z)=, u = . , , () ( ).
, , , . : Dxz = f(x + Dx, y) f(x, y) Dz = f(x, +Dy) f(x, y) .
Dz = f(x + Dx, y + Dy) f(x, y) ( D D) .
r 0(0, 0) (, ), ( , r 0).
z = f(x, y) D, 0(0, 0), D .
f(x, y) (, ) 0(0, 0), e > 0, r > 0, (, ), 0 < r, |f(x, y) A| < e. : . z = f(x, y) 0(0, 0), , (, ) 0(0, 0) , . , , .
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z = f(x, y) Dz D D 0, ..
:
, .
Dz = f(x + Dx, y + Dy) f(x, y) , f(x, y) , .
, , : (1), g1 g2 , D D .
D D z`x ¹ 0 z`y ¹ 0 , Dz D D. , dz df.
, f(x, y) , dz = f` (x, y) Dx + f`(x, y) Dy (4.1)
(4.1`), dx = Dx dy = Dy . , , (1):
(4.2)
( D D).
z = F(u, v), u = f(x, y) v = j(x, y). F(u, v) . , F(u, v), f(x,y) j(x, y) . , F(u, v) :
(4.3)
F(x, y) = 0 (2) ( ), F(x, y), Fx`(x, y) Fy`(x,y) r (, ), (2), Fy`(x,y) ¹ 0 , (4.4).
, F(x, y, z) = 0 (2`) z(x, y), (2`):
(4.4`).
: 2 + 2 + z2 R2 = 0. (4.4`) .
, , , .
( ) : (4.5). (4.5`)
(4.5``) (4.5```)
(4.5) , (4.5') - , , (4.5")- , (4.5"')- .
, , n , , n p . , z = f(x, y) (, ) , .
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, , .. , .. , , , .
z = f(x, y) , ..
(4.6).
. . F(x, y, z) = 0. 0(0, 0, z0), , 0. 0 Fx`, Fy`, Fz` , 0 . 0 , , 0 . , , 0. ( ).
Fx`(x - x0) + Fy`(y - y0) + Fz`(z -z0) = 0 (4.7).
z = f(, y), : z - z0 = fx`(x - x0) + fy`(y - y0) (4.7`).
, 0(0, 0, z0) , . `N :
(4.8),
z = f(x, y),
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z = f(x, y) (F(x, y, z) = 0). (0, 0, z0) = 0. (. 4.1) . Dy = MN = P` ( ), Dyz = TT`. , , b , P P 0 . , , a , z = f(x, y) = 0 . (4.7') 0 =D, 0 = D, , z = f(x, y) z z0 = dz, .. (, ), D D , z z = f(x, y).