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A4-format til udskrift. - Aarhus Universitet

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186 V. MATRICER<br />

✌ Effektive regneregler<br />

✌ Genkend determinant nul<br />

✌ Test determinant nul<br />

✌ Produktreglen<br />

✌ Inversreglen<br />

✌ Test inversregel og produktregel<br />

✌ Potensreglen<br />

✌ Entydig løsning<br />

✌ Test entydig løsning<br />

4.2. Nemme determinanter ☞ [LA] 8 Determinanter<br />

Eksempler<br />

Determinanten af en kvadratisk matrix<br />

• 1-matrix<br />

|a11| = a11<br />

• 2-matrix <br />

a11 a12<br />

<br />

= a11a22 − a12a21<br />

• 3-matrix<br />

<br />

<br />

<br />

<br />

<br />

<br />

<br />

<br />

<br />

<br />

<br />

<br />

a21 a22<br />

<br />

<br />

<br />

<br />

<br />

<br />

<br />

a11 a12 a13<br />

a21 a22 a23 = a11 <br />

a31 a32 a33<br />

a22 a23<br />

− a12<br />

a32 a33 a21 a23<br />

+ a13 <br />

a31 a33 a21 a22<br />

a31 a32<br />

4.3. Udregn determinanter ☞ [LA] 8 Determinanter<br />

Eksempler <br />

<br />

−1<br />

2<br />

<br />

3 4<br />

= (−1) · 4 − 2 · 3 = −10<br />

<br />

<br />

1<br />

2 3<br />

<br />

<br />

4<br />

5 6<br />

<br />

2<br />

3 0<br />

<br />

<br />

= 1 · 5<br />

6<br />

<br />

<br />

3 0<br />

− 2 · 4<br />

6<br />

<br />

<br />

2 0<br />

+ 3 · 4<br />

5<br />

<br />

2 3<br />

= (5 · 0 − 6 · 3) − 2(4 · 0 − 6 · 2)<br />

+3(4 · 3 − 5 · 2)<br />

= −18 + 24 + 6<br />

= 12<br />

4.4. Nem vej <strong>til</strong> areal ☞ [LA] 8 Determinanter<br />

Eksempel<br />

Areal<br />

<br />

<br />

<br />

a1 b1<br />

Areal = (a1 + b1)(a2 + b2) − a1a2 − b1b2 − 2a2b1<br />

= a1b2 − a2b1<br />

<br />

<br />

= <br />

a1<br />

<br />

a2<br />

<br />

<br />

b1 b2<br />

b2<br />

a2

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