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Apuntes de Variable Compleja - Carlos Lizama homepage ...

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78 CAPÍTULO 6. EJERCICIOS<br />

luego<br />

.<br />

Por lo tanto<br />

49. Evalue<br />

siempre que n ≥ −1.<br />

Solución:<br />

Res(sin 1<br />

, 0) = 1<br />

z<br />

<br />

1<br />

2πi |z|=r<br />

e w = 1 + w + w2<br />

2!<br />

e 2/z = 1 + 2<br />

z<br />

sin 1<br />

dz = 1<br />

z<br />

<br />

1<br />

z<br />

2πi |z|=r<br />

n e 2/z dz<br />

+ ...<br />

22<br />

+ + ...<br />

2!z2 zne2/z = zn + 2zn−1 + 22zn−2 2! + ...2k zn−k n!<br />

Entonces Res(z n e 2/z , 0) = 2n+1<br />

(n + 1)!<br />

50. Sea a ∈ R, a > 1. Calcule<br />

π<br />

Solución:<br />

Así<br />

π<br />

π<br />

−π<br />

<br />

1<br />

dθ =<br />

a + cos θ |z|=1<br />

−π<br />

dθ<br />

a + cosθ .<br />

1<br />

(a + z+z<br />

2<br />

<br />

2<br />

dz =<br />

)iz i |z|=1<br />

+ ...<br />

1<br />

z 2 + 2az + 1 dz<br />

Observamos que z 2 + 2az + 1 = (z + a + √ a 2 − 1)(z + a − √ a 2 − 1).<br />

−π<br />

<br />

1 4π<br />

dθ =<br />

a + cos θ 2πi |z|=1<br />

1<br />

(z + a + √ a 2 − 1)(z + a − √ a 2 − 1) =<br />

2π<br />

√ a 2 − 1

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