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

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S = Φ(A) A = (a, b) × (0, α) Φ(t, θ) =<br />

(u(t) cos θ, u(t) sin θ, v(t)) ∈ C 1 (A) <br />

Γ (0, ∞) × R <br />

γ(t) = (u(t), v(t)) <br />

<br />

<br />

∂Φ<br />

∂t<br />

<br />

<br />

A(S) =<br />

<br />

dσ2 =<br />

<br />

<br />

<br />

∂Φ<br />

∂t<br />

∧ ∂Φ<br />

∂θ<br />

<br />

<br />

<br />

dt dθ =<br />

S<br />

A<br />

<br />

∂Φ ∧ <br />

∂θ = u(t) ˙u(t) 2 + ˙v(t) 2 u(t) > 0<br />

b<br />

= α u(t)<br />

a<br />

˙u(t) 2 + ˙v(t) 2 dt.<br />

<br />

<br />

<br />

A(S) = α<br />

Γ<br />

x dσ1.<br />

Γ l(γ) <br />

A(S) = α l(γ) 1<br />

<br />

x dσ1 = α l(γ) xb<br />

l(γ) Γ<br />

xb Γ <br />

<br />

α Γ <br />

Γ <br />

γ <br />

<br />

x(θ) = ρ(θ) cos θ = a (1 + cos θ) cos θ<br />

θ ∈ (0, 2π) .<br />

y(θ) = ρ(θ) sin θ = a (1 + cos θ) sin θ<br />

γ <br />

<br />

2π<br />

<br />

lungh (γ) = ds := x<br />

γ<br />

0<br />

′2<br />

+ y ′2<br />

dθ .<br />

<br />

<br />

′ ′ ′ ′ x (θ) = ρ (θ) cos θ − ρ(θ) sin θy (θ) = ρ (θ) sin θ + ρ(θ) cos θ ,

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