Calculus 3 : Calculus 3

Study concepts, example questions & explanations for Calculus 3

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Example Questions

Example Question #632 : Vectors And Vector Operations

Find the determinant of the matrix \(\displaystyle A=\begin{vmatrix} 3&13 &15 \\ 20& -4&7 \\2 &11 &14 \end{vmatrix}\)

Possible Answers:

\(\displaystyle -437\)

\(\displaystyle 6479\)

\(\displaystyle -3432\)

\(\displaystyle -211\)

\(\displaystyle 803\)

Correct answer:

\(\displaystyle -437\)

Explanation:

The determinant of a 3x3 matrix can be found via a means of reduction into three 2x2 matrices as follows:

\(\displaystyle det\begin{vmatrix} a&b&c \\ d&e&f\\g&h&i \end{vmatrix}=a\begin{Vmatrix} e&f \\ h&i \end{Vmatrix}-b\begin{Vmatrix} d&f \\ g&i \end{Vmatrix}+c\begin{Vmatrix} d&e \\ g&h \end{Vmatrix}\)

These can then be further reduced via the method of finding the determinant of a 2x2 matrix:

\(\displaystyle det\begin{vmatrix} a&b&c \\ d&e&f\\g&h&i \end{vmatrix}=a(ei-fh)-b(di-fg)+c(dh-eg)\)

For the matrix \(\displaystyle A=\begin{vmatrix} 3&13 &15 \\ 20& -4&7 \\2 &11 &14 \end{vmatrix}\)

The determinant is thus:

\(\displaystyle |A|=3[-4(14)-11(7)]-13[20(14)-2(7)]+15[20(11)-2(-4)]=-437\)

Example Question #631 : Vectors And Vector Operations

Find the determinant of the matrix \(\displaystyle A=\begin{vmatrix} 4&3 &4 \\2 &0 &6 \\0 &8 &3 \end{vmatrix}\)

Possible Answers:

\(\displaystyle 404\)

\(\displaystyle 86\)

\(\displaystyle -215\)

\(\displaystyle -319\)

\(\displaystyle -146\)

Correct answer:

\(\displaystyle -146\)

Explanation:

The determinant of a 3x3 matrix can be found via a means of reduction into three 2x2 matrices as follows:

\(\displaystyle det\begin{vmatrix} a&b&c \\ d&e&f\\g&h&i \end{vmatrix}=a\begin{Vmatrix} e&f \\ h&i \end{Vmatrix}-b\begin{Vmatrix} d&f \\ g&i \end{Vmatrix}+c\begin{Vmatrix} d&e \\ g&h \end{Vmatrix}\)

These can then be further reduced via the method of finding the determinant of a 2x2 matrix:

\(\displaystyle det\begin{vmatrix} a&b&c \\ d&e&f\\g&h&i \end{vmatrix}=a(ei-fh)-b(di-fg)+c(dh-eg)\)

For the matrix \(\displaystyle A=\begin{vmatrix} 4&3 &4 \\2 &0 &6 \\0 &8 &3 \end{vmatrix}\)

The determinant is thus:

\(\displaystyle |A|=4[0(3)-8(6)]-3[2(3)-0(6)]+4[2(8)-0(0)]=-146\)

Example Question #47 : Matrices

Find the determinant of the matrix \(\displaystyle A=\begin{vmatrix} 7& 11\\3 &23 \end{vmatrix}\)

Possible Answers:

\(\displaystyle -232\)

\(\displaystyle 161\)

\(\displaystyle 194\)

\(\displaystyle 128\)

\(\displaystyle 275\)

Correct answer:

\(\displaystyle 128\)

Explanation:

The determinant of a 2x2 matrix can be found by cross multiplying terms as follows:

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

For the matrix \(\displaystyle A=\begin{vmatrix} 7& 11\\3 &23 \end{vmatrix}\)

The determinant is thus:

\(\displaystyle |A|=161-33=128\)

Example Question #48 : Matrices

Find the determinant of the matrix \(\displaystyle A=\begin{vmatrix} -4& -3\\-1 & -2\end{vmatrix}\)

Possible Answers:

\(\displaystyle -2\)

\(\displaystyle 5\)

\(\displaystyle 15\)

\(\displaystyle 14\)

\(\displaystyle 10\)

Correct answer:

\(\displaystyle 5\)

Explanation:

The determinant of a 2x2 matrix can be found by cross multiplying terms as follows:

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

For the matrix \(\displaystyle A=\begin{vmatrix} -4& -3\\-1 & -2\end{vmatrix}\)

The determinant is thus:

\(\displaystyle |A|=8-3=5\)

Example Question #49 : Matrices

Find the determinant of the matrix \(\displaystyle A=\begin{vmatrix}12 &4 \\30 &10 \end{vmatrix}\)

Possible Answers:

\(\displaystyle -252\)

\(\displaystyle 400\)

\(\displaystyle 320\)

\(\displaystyle 348\)

\(\displaystyle 0\)

Correct answer:

\(\displaystyle 0\)

Explanation:

The determinant of a 2x2 matrix can be found by cross multiplying terms as follows:

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

For the matrix \(\displaystyle A=\begin{vmatrix}12 &4 \\30 &10 \end{vmatrix}\)

The determinant is thus:

\(\displaystyle |A|=120-120=0\)

This result is due to the columns being linearly dependent, i.e. multiples of each other. The first column is three times the second column.

Example Question #50 : Matrices

Find the determinant of the matrix \(\displaystyle A=\begin{vmatrix} 1& 3\\7 &13 \end{vmatrix}\)

Possible Answers:

\(\displaystyle 0\)

\(\displaystyle 34\)

\(\displaystyle -32\)

\(\displaystyle 46\)

\(\displaystyle -8\)

Correct answer:

\(\displaystyle -8\)

Explanation:

The determinant of a 2x2 matrix can be found by cross multiplying terms as follows:

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

For the matrix \(\displaystyle A=\begin{vmatrix} 1& 3\\7 &13 \end{vmatrix}\)

The determinant is thus:

\(\displaystyle |A|=13-21=-8\)

Example Question #51 : Matrices

Find the determinant of the matrix \(\displaystyle A=\begin{vmatrix} -15& -2\\ 4& -1\end{vmatrix}\)

Possible Answers:

\(\displaystyle 7\)

\(\displaystyle 0\)

\(\displaystyle 34\)

\(\displaystyle 23\)

\(\displaystyle 26\)

Correct answer:

\(\displaystyle 23\)

Explanation:

The determinant of a 2x2 matrix can be found by cross multiplying terms as follows:

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

For the matrix \(\displaystyle A=\begin{vmatrix} -15& -2\\ 4& -1\end{vmatrix}\)

The determinant is thus:

\(\displaystyle |A|=15-(-8)=23\)

Example Question #641 : Vectors And Vector Operations

Find the determinant of the matrix \(\displaystyle A=\begin{vmatrix} -8&7 \\2 & -3\end{vmatrix}\)

Possible Answers:

\(\displaystyle 0\)

\(\displaystyle 10\)

\(\displaystyle -50\)

\(\displaystyle 5\)

\(\displaystyle -62\)

Correct answer:

\(\displaystyle 10\)

Explanation:

The determinant of a 2x2 matrix can be found by cross multiplying terms as follows:

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

For the matrix \(\displaystyle A=\begin{vmatrix} -8&7 \\2 & -3\end{vmatrix}\)

The determinant is thus:

\(\displaystyle |A|=24-14=10\)

Example Question #53 : Matrices

Find the matrix product of \(\displaystyle A\times b\), where \(\displaystyle A=\begin{vmatrix} 2&0 \\3 &1 \end{vmatrix}\) and \(\displaystyle b=\begin{vmatrix} 4\\-2 \end{vmatrix}\) .

Possible Answers:

\(\displaystyle \begin{vmatrix}0\\10 \end{vmatrix}\)

\(\displaystyle \begin{vmatrix}10\\8 \end{vmatrix}\)

\(\displaystyle \begin{vmatrix}8\\0 \end{vmatrix}\)

\(\displaystyle \begin{vmatrix}10\\10 \end{vmatrix}\)

\(\displaystyle \begin{vmatrix}8\\10 \end{vmatrix}\)

Correct answer:

\(\displaystyle \begin{vmatrix}8\\10 \end{vmatrix}\)

Explanation:

In order to multiply two matrices, \(\displaystyle A\times b\), the respective dimensions of each must be of the form \(\displaystyle m \times n\) and \(\displaystyle n \times p\) to create an \(\displaystyle m\times p\) (notation is rows x columns) matrix. Unlike the multiplication of individual values, the order of the matrices does matter.

\(\displaystyle (A\times b \neq b \times A)\)

For a multiplication of the form

\(\displaystyle \begin{vmatrix} A_{1,1}&A_{1,2} &... &A_{1,n} \\ A_{2,1}&A_{2,2} &.. &A_{2,n} \\ ...& ...&... &... \\ A_{m,1}&A_{m,2} &... &A_{m,n} \end{vmatrix}\times \begin{vmatrix} b_{1,1}&b_{1,2} &... &b_{1,p} \\ b_{2,1}&b_{2,2} &... &b_{2,p} \\ ...&... &... &... \\ b_{n,1}&b_{n,2} &... &b_{n,p} \end{vmatrix}\)

The resulting matrix is

\(\displaystyle \begin{vmatrix} A_{1,1}b_{1,1}+A_{1,2}b_{2,1}+...+A_{1,n}b_{n,1}&... &A_{1,1}b_{1,p}+A_{1,2}b_{2,p}+...+A_{1,n}b_{n,p} \\ ...&... &... \\ A_{m,1}b_{1,1}+A_{m,2}b_{2,1}+...+A_{m,n}b_{n,1}&... &A_{m,1}b_{1,p}+A_{m,2}b_{2,p}+...+A_{m,n}b_{n,p} \end{vmatrix}\)

The notation may be daunting but numerical examples may elucidate.

We're told that \(\displaystyle A=\begin{vmatrix} 2&0 \\3 &1 \end{vmatrix}\) and \(\displaystyle b=\begin{vmatrix} 4\\-2 \end{vmatrix}\) 

The resulting matrix product is then:

\(\displaystyle A\times b = \begin{vmatrix}8+0\\ 12-2\end{vmatrix}=\begin{vmatrix}8\\10 \end{vmatrix}\)

Example Question #54 : Matrices

Find the matrix product of \(\displaystyle A\times b\), where \(\displaystyle A=\begin{vmatrix} 3&0 \\0 &3 \end{vmatrix}\) and \(\displaystyle b=\begin{vmatrix} 1\\4 \end{vmatrix}\) .

Possible Answers:

\(\displaystyle \begin{vmatrix}3\\4 \end{vmatrix}\)

\(\displaystyle \begin{vmatrix}0\\0 \end{vmatrix}\)

\(\displaystyle \begin{vmatrix}3\\12 \end{vmatrix}\)

\(\displaystyle \begin{vmatrix}0\\12 \end{vmatrix}\)

\(\displaystyle \begin{vmatrix}12\\4 \end{vmatrix}\)

Correct answer:

\(\displaystyle \begin{vmatrix}3\\12 \end{vmatrix}\)

Explanation:

In order to multiply two matrices, \(\displaystyle A\times b\), the respective dimensions of each must be of the form \(\displaystyle m \times n\) and \(\displaystyle n \times p\) to create an \(\displaystyle m\times p\) (notation is rows x columns) matrix. Unlike the multiplication of individual values, the order of the matrices does matter.

\(\displaystyle (A\times b \neq b \times A)\)

For a multiplication of the form

\(\displaystyle \begin{vmatrix} A_{1,1}&A_{1,2} &... &A_{1,n} \\ A_{2,1}&A_{2,2} &.. &A_{2,n} \\ ...& ...&... &... \\ A_{m,1}&A_{m,2} &... &A_{m,n} \end{vmatrix}\times \begin{vmatrix} b_{1,1}&b_{1,2} &... &b_{1,p} \\ b_{2,1}&b_{2,2} &... &b_{2,p} \\ ...&... &... &... \\ b_{n,1}&b_{n,2} &... &b_{n,p} \end{vmatrix}\)

The resulting matrix is

\(\displaystyle \begin{vmatrix} A_{1,1}b_{1,1}+A_{1,2}b_{2,1}+...+A_{1,n}b_{n,1}&... &A_{1,1}b_{1,p}+A_{1,2}b_{2,p}+...+A_{1,n}b_{n,p} \\ ...&... &... \\ A_{m,1}b_{1,1}+A_{m,2}b_{2,1}+...+A_{m,n}b_{n,1}&... &A_{m,1}b_{1,p}+A_{m,2}b_{2,p}+...+A_{m,n}b_{n,p} \end{vmatrix}\)

The notation may be daunting but numerical examples may elucidate.

We're told that \(\displaystyle A=\begin{vmatrix} 3&0 \\0 &3 \end{vmatrix}\) and \(\displaystyle b=\begin{vmatrix} 1\\4 \end{vmatrix}\)

The resulting matrix product is then:

\(\displaystyle A\times b = \begin{vmatrix} 3+0\\0+12 \end{vmatrix}=\begin{vmatrix}3\\12 \end{vmatrix}\)

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