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MATEMATIKA 1 skripta studij: Biotehnologija i Prehrambena ... - PBF

MATEMATIKA 1 skripta studij: Biotehnologija i Prehrambena ... - PBF

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⎡ ⎤ ⎡ ⎤<br />

a 11 a 12 a 14 a 11 a 12 a 14<br />

Rješenje: M 23 = ⎢<br />

⎣ a 31 a 32 a 34<br />

⎥<br />

⎦ , M 33 = ⎢<br />

⎣ a 21 a 22 a 24<br />

⎥<br />

⎦ ,<br />

a 41 a 42 a 44 a 41 a 42 a 44<br />

A 23 = (−1) 2+3 detM 23 = −detM 23 , A 33 = (−1) 3+3 detM 33 = detM 33 .<br />

−2 1 3<br />

Zadatak 10 Izračunajte D =<br />

5 4 2<br />

∣ −3 0 5<br />

a) razvojem po drugom retku<br />

b) razvojem po trećem stupcu<br />

∣<br />

Rješenje: a)<br />

D = 5(−1) 2+1 ∣ ∣∣∣∣<br />

1 3<br />

0 5<br />

∣ ∣ ∣∣∣∣ −2 3<br />

∣∣∣∣ −2 1<br />

∣ +4(−1)2+2 −3 5 ∣ +2(−1)2+3 −3 0<br />

= −5(5−0)+4(−10+9)−2(0+3) = −35.<br />

∣<br />

b)<br />

D = 3(−1) 1+3 ∣ ∣∣∣∣<br />

5 4<br />

−3 0<br />

∣ ∣ ∣∣∣∣ −2 1<br />

∣∣∣∣ −2 1<br />

∣ +2(−1)2+3 −3 0 ∣ +5(−1)3+3 5 4<br />

= 3(0+12)−2(0+3)+5(−8−5) = −35.<br />

∣<br />

[ ] [ ]<br />

1 2 4 3<br />

Zadatak 11 Neka je A = i B = .<br />

3 4 2 1<br />

a) Vrijedi li AB = BA?<br />

b) Vrijedi li det(AB) = det(BA) = detA·detB?<br />

c) Vrijedi li formula za kvadrat zbroja, tj. (A+B) 2 = A 2 +2AB +B 2 ?<br />

Rješenje:<br />

[<br />

8 5<br />

a) AB =<br />

20 13<br />

] [<br />

13 20<br />

, BA =<br />

5 8<br />

11<br />

]<br />

. Dakle, AB ≠ BA.

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