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Introduç˜ao `a´Algebra Linear com o gnu-Octave - Departamento de ...

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2.4. DETERMINANTES 45<br />

00 11<br />

00 11<br />

00 11<br />

00 11<br />

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00000000000<br />

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00000000000<br />

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00000000000<br />

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00000000000<br />

11111111111<br />

00000000000<br />

11111111111<br />

00000000000<br />

11111111111<br />

00000000000<br />

11111111111<br />

00 11 00000000000<br />

1111111111100<br />

00 11<br />

00 11<br />

Figura 2.1: Esquema do cálculo do <strong>de</strong>terminante <strong>de</strong> matrizes <strong>de</strong> or<strong>de</strong>m 2<br />

Seja agora A =<br />

⎡<br />

⎢<br />

⎣<br />

⎤<br />

a 11 a 12 a 13<br />

⎥<br />

a 21 a 22 a 23<br />

a 31 a 32 a 33<br />

⎦. Recor<strong>de</strong> que S 3 tem 6 elementos. No quadro seguinte,<br />

indicamos, respectivamente, a permutação σ ∈ S 3 , o seu sinal, e o produto a 1σ(1) a 2σ(2) · · · a nσ(n) .<br />

Obtemos, assim,<br />

Permutação σ ∈ S 3 sgn(σ) a 1σ(1) a 2σ(2) · · · a nσ(n)<br />

(1 2 3) +1 a 11 a 22 a 33<br />

(2 3 1) +1 a 12 a 23 a 31<br />

(3 1 2) +1 a 13 a 21 a 32<br />

(1 3 2) −1 a 11 a 23 a 32<br />

(2 1 3) −1 a 12 a 21 a 33<br />

(3 2 1) −1 a 11 a 22 a 31<br />

|A| = a 11 a 22 a 33 + a 12 a 23 a 31 + a 13 a 21 a 32<br />

−a 11 a 23 a 32 − a 12 a 21 a 33 − a 11 a 22 a 31<br />

Para fácil memorização, po<strong>de</strong>-se recorrer ao esquema apresentado <strong>de</strong> seguida.<br />

000000000000000000000<br />

111111111111111111111<br />

00000000000000000000<br />

11111111111111111111<br />

000000000000000000000<br />

111111111111111111111<br />

00000000000000000000<br />

11111111111111111111<br />

00000000000000000000000<br />

11111111111111111111111<br />

000000000000000000000<br />

111111111111111111111<br />

00000000000000000000<br />

11111111111111111111<br />

00000000000000000000000<br />

11111111111111111111111<br />

000000000000000000000<br />

111111111111111111111<br />

00000000000000000000<br />

11111111111111111111<br />

00000000000000000000000<br />

11111111111111111111111<br />

000000000000000000000<br />

111111111111111111111<br />

00000000000000000000<br />

11111111111111111111<br />

00000000000000000000000<br />

11111111111111111111111<br />

000000000000000000000<br />

111111111111111111111<br />

00000000000000000000<br />

11111111111111111111<br />

00000000000000000000000<br />

11111111111111111111111<br />

000000000000000000000<br />

111111111111111111111<br />

00 11<br />

00 11<br />

00000000000000000000<br />

11111111111111111111<br />

00000000000000000000000<br />

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000000000000000000000<br />

111111111111111111111<br />

00000000000000000000<br />

11111111111111111111<br />

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11111111111111111111111<br />

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00000000000000000000<br />

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00000000000000000000000<br />

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000000000000000000000<br />

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00 11<br />

00000000000000000000<br />

11111111111111111111<br />

00000000000000000000000<br />

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000000000000000000000<br />

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00000000000000000000<br />

11111111111111111111<br />

00000000000000000000000<br />

11111111111111111111111<br />

000000000000000000000<br />

111111111111111111111<br />

00000000000000000000<br />

11111111111111111111<br />

00000000000000000000000<br />

11111111111111111111111<br />

000000000000000000000<br />

111111111111111111111<br />

00000000000000000000<br />

11111111111111111111<br />

00000000000000000000000<br />

11111111111111111111111<br />

000000000000000000000<br />

111111111111111111111<br />

00000000000000000000<br />

11111111111111111111<br />

00000000000000000000000<br />

11111111111111111111111<br />

000000000000000000000<br />

111111111111111111111<br />

00000000000000000000<br />

11111111111111111111<br />

00000000000000000000000<br />

11111111111111111111111<br />

000000000000000000000<br />

111111111111111111111<br />

00000000000000000000<br />

11111111111111111111<br />

00000000000000000000000<br />

11111111111111111111111<br />

000000000000000000000<br />

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00000000000000000000000<br />

11111111111111111111111<br />

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111111111111111111111<br />

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11111111111111111111<br />

00000000000000000000000<br />

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000000000000000000000<br />

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00000000000000000000<br />

11111111111111111111<br />

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00000000000000000000000<br />

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000000000000000000000<br />

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11111111111111111111111<br />

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00000000000000000000000<br />

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00 11<br />

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111111111111111111111<br />

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11111111111111111111111<br />

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00 11 000000000000000000000<br />

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00 11<br />

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00000000000000000000000<br />

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111111111111111111111<br />

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00 11 000000000000000000000<br />

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00 11 000000000000000000000<br />

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00 11<br />

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00000000000000000000000<br />

11111111111111111111111<br />

00000000000000000000000<br />

11111111111111111111111<br />

00000000000000000000000<br />

11111111111111111111111<br />

00000000000000000000000<br />

11111111111111111111111<br />

Figura 2.2: Esquema do cálculo do <strong>de</strong>terminante <strong>de</strong> matrizes <strong>de</strong> or<strong>de</strong>m 3, ou a Regra <strong>de</strong><br />

Sarrus<br />

2.4.2 Proprieda<strong>de</strong>s<br />

São consequência da <strong>de</strong>finição os resultados que <strong>de</strong> seguida apresentamos, dos quais omitimos<br />

a <strong>de</strong>monstração.<br />

Teorema 2.4.2. Seja A uma matriz quadrada.

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