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Esercizi svolti di analisi reale e complessa - Dipartimento di ...

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(⇐=) i = 1, . . . , m fi x0<br />

<br />

∀ ε > 0 ∃ δi = δi(ε) > 0 : |x − x0| < δ =⇒ |fi(x) − fi(x0)| < ε<br />

√ m .<br />

<br />

δ = δ(ε) = min{δ1(ε), . . . , δm(ε)} ;<br />

|x − x0| ≤ δ <br />

|f(x) − f(x0| ≤ √ m max<br />

i=1,...,m {|fi(x) − fi(x0)|} ≤<br />

≤ √ m ε<br />

√ m = ε .<br />

<br />

| · | Rn x, y ∈ B1(0) <br />

f(x) − f(y) =<br />

<br />

<br />

<br />

<br />

<br />

<br />

1 1 <br />

− <br />

2 − |x| 2 − |y| =<br />

1 1<br />

−<br />

2 − |x| 2 − |y| ,<br />

≤<br />

<br />

<br />

<br />

<br />

sin<br />

n<br />

i=1<br />

xi<br />

<br />

<br />

<br />

<br />

−<br />

<br />

<br />

<br />

<br />

sin<br />

n<br />

i=1<br />

yi<br />

<br />

<br />

<br />

.<br />

<br />

<br />

<br />

<br />

<br />

2 − |y| − 2 + |x| <br />

<br />

(2<br />

− |x|)(2 − |y|)) =<br />

| |x| − |y| |<br />

(2 − |x|)(2 − |y|) ≤<br />

|x − y|<br />

≤ |x − y| .<br />

(2 − |x|)(2 − |y|)<br />

<br />

m N <br />

xm =<br />

ym =<br />

<br />

| |x| − |y| | ≤ |x − y| x, y ∈ R n <br />

2 − |x| ≥ 1 x ∈ B1(0) <br />

<br />

1 − 1<br />

<br />

, 0, . . . , 0<br />

2m<br />

<br />

1 − 1<br />

<br />

, 0, . . . , 0<br />

m

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