в̲ί Ҳ ֲ.
y=f(x) [a, b]. f(x) =0, :
1) =f(x0) ( ).
f(x) =0, :
2) ∀ε>0 ∃δ(ε)>0 ∀ x ∈ [a,b] |x-x0|< δ |f(x)-f(x0)|< ε ( ( ´´ε δ ´´).
3) ∀ {xn}->x0 (∀n ∈ N, xn ∈ [a,b] {f(x)}-> f(x0) ( ( )).
f(x) , , , ∀ x ∈ X ∀ ε>0 ∃δ(ε,x)>0:
∀ x´ ∈ X, |x-x´|< δ: |f(x)-f(x´)|< ε.
y=f(x) , ∀ ε>0 ∃δ(ε): ∀ , x ´ ∈ X |x- x ´|< δ: |f(x)- f(x ´)|< ε.
³, δ x ∈ X ( ε). δ . ( δ ).
1
y=f(x)=x2 X =[-l; l], l- const(l>0)
, . , ∀ ε>0 ∃δ(ε)>0: ∀ x´, x´ ∈ [-l;l], |x´-x´´|< δ, |(x´)2 - (x´´)2|< ε.
:
|(x´)2-(x´´)2|=|x´-x´´|*|x´+x´´|<|x´-x´´|*||x´|+|x´´||< δ*2l= ε, |x´ - x´´|< δ, |x´ + x´´|<2* δ.
, δ=
2
y=f(x) = x2 X = (-∞; +∞)
1) ∀→∃
2) ∃→∀
3) <→≥
∃ ε>0: ∀ δ>0 ∃ x´, x´ ∈ (-∞; +∞), |x´-x´´|< δ |(x´)2-(x´´)2|≥ ε
x´= , x´´= + |x´-x´´|= < δ
|(x´)2-(x´´)2|=|x´-x´´|*|x´ + x´´|= ≥1= ε
∃ ε=1: ∀δ>0, ∃ , + ∈ (-∞; +∞), |x´ - x´´|< δ, |(x´)2-(x´´)2|≥ ε. , , .
f(x) [a;b], .
( )
, f(x) [a;b], . , , ∀ε>0 ∃δ(ε)>0 ∃ x´, x´´ ∈ [a,b] |x´ - x´´|< δ |f(x´) - f(x´´)|≥ ε.
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³ { δ n}→0 (∀ n ∈ N δ n>0) , 0.
(, δ n= ). ∀ δ n>0 xn´, xn´´ ∈ [a,b], |xn´-xn´´|< δn |f(xn´)-f(xn´´)|≥ ε (1) (, (1) ).
: {xn´}, {xn´´}. {xn´} [a, b], - {xnk´}.
=x0 (2), , x0 ∈ [a,b].
|xnk´´-x0|=|(xnk´´ - xnk´)+(xnk´-x0)| |xnk´´ - xnk´|+|xnk´ - x0|→0, |xnk´´- xnk´|, |xnk´-x0|→ 0 ( k→∞). , →x0 (3). f(x) [a,b], x0, .
, ,
) = f(x0), ) = f(x0). , |f(x´nk)-f(x´´nk)|→0( k→∞)(4). (4) (1), {xn} {xnk}. .
f(x) [a, b] ω=M-m, M=sup x∈ [a,b] f(x), m=inf x∈ [a,b]f(x).
f(x) [a,b]. ∀ε>0 ∃δ >0 , [a, b] , δ, f(x) ε.
f(x)=x2 [-l, +l], , (, ). : y= , [0,1].