Linear Algebra : The Determinant

Study concepts, example questions & explanations for Linear Algebra

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Example Questions

Example Question #1 : The Determinant

Calculate the determinant of matrix A where

\(\displaystyle A = \begin{bmatrix} 5&4 \\ 1&2 \\ 0&7 \end{bmatrix}\)

Possible Answers:

45

Not Possible 

0

-50

10

Correct answer:

Not Possible 

Explanation:

The matrix must be square to calculate its determinant, therefore, it is not possible to calculate the determinant for this matrix.  

Example Question #2 : The Determinant

Calculate the determinant of matrix A where,

 \(\displaystyle A=\begin{bmatrix} 4&1 \\ 5& 3 \end{bmatrix}\)

Possible Answers:

0

-7

7

12

17

Correct answer:

7

Explanation:

To calculate the determinant of a 2x2 matrix, we can use the equation \(\displaystyle a_{^{11}}a_{^{22}}-a_{^{12}}a_{^{21}}\)

Example Question #3 : The Determinant

Calculate the determinant of matrix A where, 

\(\displaystyle A=\begin{bmatrix} 8&-8 \\ 51&12 \end{bmatrix}\)

Possible Answers:

-504

504

54

0

-315

Correct answer:

504

Explanation:

To calculate the determinant of a 2x2 matrix, we can use the equation \(\displaystyle a_{^{11}}a_{^{22}}-a_{^{12}}a_{^{21}}\)

Example Question #4 : The Determinant

Calculate the determinant of matrix A where, 

\(\displaystyle A=\begin{bmatrix} 8&6 \\ 0&2 \end{bmatrix}\)

Possible Answers:

15

0

-15

16

17

Correct answer:

16

Explanation:

To calculate the determinant of a 2x2 matrix, we can use the equation \(\displaystyle a_{^{11}}a_{^{22}}-a_{^{12}}a_{^{21}}\)

Example Question #5 : The Determinant

Calculate the determinant of matrix A where,

\(\displaystyle A=\begin{bmatrix} 2&5 &6 \\ 2&1 &0 \\ 5&3 &4 \end{bmatrix}\)

Possible Answers:

-26

0

-24

26

15

Correct answer:

-26

Explanation:

Calculating the determinant of a 3x3 matrix is more difficult than a 2x2 matrix.  To calculate the determinant of a 3x3 matrix, we use the following \(\displaystyle \left | A\right |=a_{11}(a_{22}a_{33}-a_{23}a_{32})-a_{12}(a_{21}a_{33}-a_{23}a_{31})+a_{13}(a_{21}a_{32}-a_{22}a_{31})\)

Example Question #6 : The Determinant

Calculate the determinant of matrix A where,

\(\displaystyle A=\begin{bmatrix} -5&7 &10 \\ -20&15 &2 \\ 0& 3& 8 \end{bmatrix}\)

Possible Answers:

49

-49

-50

0

50

Correct answer:

-50

Explanation:

Calculating the determinant of a 3x3 matrix is more difficult than a 2x2 matrix.  To calculate the determinant of a 3x3 matrix, we use the following \(\displaystyle \left | A\right |=a_{11}(a_{22}a_{33}-a_{23}a_{32})-a_{12}(a_{21}a_{33}-a_{23}a_{31})+a_{13}(a_{21}a_{32}-a_{22}a_{31})\)

Example Question #7 : The Determinant

Calculate the determinant of \(\displaystyle \begin{bmatrix} 5&-2 \\ 1&3 \end{bmatrix}\).

Possible Answers:

\(\displaystyle 6\)

\(\displaystyle 17\)

\(\displaystyle -1\)

\(\displaystyle 13\)

Correct answer:

\(\displaystyle 17\)

Explanation:

By definition,

\(\displaystyle \begin{vmatrix} a&b \\ c&d \end{vmatrix}= a(d)-b(c)\),

therefore,

\(\displaystyle \begin{vmatrix} 5&-2 \\ 1&3 \end{vmatrix}= 5(3)-1(-2)= 17\).

Example Question #8 : The Determinant

Calculate the determinant of \(\displaystyle \begin{bmatrix} 1&3 &1 \\ 0& 2&0 \\ 4&8 &2 \end{bmatrix}\)

Possible Answers:

\(\displaystyle 0\)

\(\displaystyle 21\)

\(\displaystyle -4\)

\(\displaystyle 4\)

Correct answer:

\(\displaystyle -4\)

Explanation:

For simplicity, we will find the determinant by expanding along the second row.  Consider the following:

\(\displaystyle \begin{vmatrix} 1&3 &1 \\ 0& 2&0 \\ 4&8 &2 \end{vmatrix}= -0[3(2)-1(8)]+2[1(2)-1(4)]-0[1(8)-3(4)]= -4\)

Example Question #8 : The Determinant

Calculate the determinant of \(\displaystyle \begin{bmatrix} 1&2 \\ 3&6 \end{bmatrix}\).

Possible Answers:

\(\displaystyle 16\)

\(\displaystyle 0\)

\(\displaystyle 12\)

\(\displaystyle -4\)

Correct answer:

\(\displaystyle 0\)

Explanation:

By definition,

\(\displaystyle \begin{vmatrix} a&b \\ c&d \end{vmatrix}= ad-bc \Rightarrow \begin{vmatrix} 1&2 \\ 3&6 \end{vmatrix} = 1(6)- 2(3) = 0\).

Example Question #7 : The Determinant

Calculate the determinant of matrix A. 

 \(\displaystyle A =\begin{bmatrix} 5&3 \\ 6&4 \end{bmatrix}\)

Possible Answers:

\(\displaystyle -2\)

\(\displaystyle 38\)

\(\displaystyle 2\)

\(\displaystyle 1\)

Not possible

Correct answer:

\(\displaystyle 2\)

Explanation:

In order to find the determinant of a 2x2 matrix, compute \(\displaystyle det A= a_{11}a_{22}-a_{12}a_{21}\) :

\(\displaystyle = 5(4)-3(6)\)

\(\displaystyle =20-18\)

\(\displaystyle =2\)

 

 

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