Calculus 3 : Matrices

Study concepts, example questions & explanations for Calculus 3

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Example Questions

Example Question #685 : Vectors And Vector Operations

Find the determinant of the matrix \(\displaystyle A=\begin{vmatrix} 15& -15& -15\\10 &-13 &-9 \\11 &3 &-1 \end{vmatrix}\)

Possible Answers:

\(\displaystyle 880\)

\(\displaystyle -702\)

\(\displaystyle -660\)

\(\displaystyle 1354\)

\(\displaystyle -2104\)

Correct answer:

\(\displaystyle -660\)

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 \(\displaystyle A=\begin{vmatrix} 15& -15& -15\\10 &-13 &-9 \\11 &3 &-1 \end{vmatrix}\)

The determinant is thus:

\(\displaystyle {|A|=15[-13(-1)-3(-9)]-(-15)[10(-1)-11(-9)]+(-15)[10(3)-11(-13)]=-660}\)

Example Question #686 : Vectors And Vector Operations

Find the determinant of the matrix \(\displaystyle A=\begin{vmatrix} 5& 0&-5 \\-7 &8 &-6 \\ -2&-9 &4 \end{vmatrix}\)

Possible Answers:

\(\displaystyle 809\)

\(\displaystyle 271\)

\(\displaystyle -505\)

\(\displaystyle -483\)

\(\displaystyle -1224\)

Correct answer:

\(\displaystyle -505\)

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 \(\displaystyle A=\begin{vmatrix} 5& 0&-5 \\-7 &8 &-6 \\ -2&-9 &4 \end{vmatrix}\)

The determinant is thus:

\(\displaystyle {|A|=5[8(4)-(-9)(-6)]-0[-7(4)-(-2)(-6)]+(-5)[-7(-9)-(-2)(8)]=-505}\)

Example Question #687 : Vectors And Vector Operations

Find the determinant of the matrix \(\displaystyle A=\begin{vmatrix}-6 &-9 &-5 \\-1 &8 &6 \\-3 &6 & 7\end{vmatrix}\)

Possible Answers:

\(\displaystyle -815\)

\(\displaystyle -111\)

\(\displaystyle 384\)

\(\displaystyle 444\)

\(\displaystyle -290\)

Correct answer:

\(\displaystyle -111\)

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 \(\displaystyle A=\begin{vmatrix}-6 &-9 &-5 \\-1 &8 &6 \\-3 &6 & 7\end{vmatrix}\)

The determinant is thus:

\(\displaystyle {|A|=-6[8(7)-6(6)]-(-9)[-1(7)-(-3)(6)]+(-5)[-1(6)-(-3)(8)]=-111}\)

Example Question #688 : Vectors And Vector Operations

Find the determinant of the matrix \(\displaystyle A=\begin{vmatrix} 9&8 &-5 \\2 &-5 &7 \\8 &9 &8 \end{vmatrix}\)

Possible Answers:

\(\displaystyle 903\)

\(\displaystyle 1544\)

\(\displaystyle 477\)

\(\displaystyle -1113\)

\(\displaystyle -897\)

Correct answer:

\(\displaystyle -897\)

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 \(\displaystyle A=\begin{vmatrix} 9&8 &-5 \\2 &-5 &7 \\8 &9 &8 \end{vmatrix}\)

The determinant is thus:

\(\displaystyle |A|=9[-5(8)-9(7)]-8[2(8)-8(7)]+(-5)[2(9)-8(-5)]=-897\)

Example Question #689 : Vectors And Vector Operations

Find the determinant of the matrix \(\displaystyle A=\begin{vmatrix} 2& -6&8 \\4 &-4 &2 \\8 &0 & -5\end{vmatrix}\)

Possible Answers:

\(\displaystyle -288\)

\(\displaystyle -192\)

\(\displaystyle 80\)

\(\displaystyle 405\)

\(\displaystyle 311\)

Correct answer:

\(\displaystyle 80\)

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 \(\displaystyle A=\begin{vmatrix} 2& -6&8 \\4 &-4 &2 \\8 &0 & -5\end{vmatrix}\)

The determinant is thus:

\(\displaystyle |A|=2[-4(-5)-0(2)]-(-6)[4(-5)-8(2)]+8[4(0)-8(-4)]=80\)

Example Question #681 : Vectors And Vector Operations

Find the determinant of the matrix \(\displaystyle A=\begin{vmatrix} -5&5 &-6 \\3 &-2 &8 \\2 &3 &1 \end{vmatrix}\)

Possible Answers:

\(\displaystyle 117\)

\(\displaystyle -42\)

\(\displaystyle -95\)

\(\displaystyle 13\)

\(\displaystyle -285\)

Correct answer:

\(\displaystyle 117\)

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 \(\displaystyle A=\begin{vmatrix} -5&5 &-6 \\3 &-2 &8 \\2 &3 &1 \end{vmatrix}\)

The determinant is thus:

\(\displaystyle |A|=-5[-2(1)-3(8)]-5[3(1)-2(8)]+(-6)[3(3)-2(-2)]=117\)

Example Question #691 : Vectors And Vector Operations

Find the determinant of the matrix \(\displaystyle A=\begin{vmatrix} 5&-5 &-3 \\-5 &5 &-7 \\7 &9 &5 \end{vmatrix}\)

Possible Answers:

\(\displaystyle 972\)

\(\displaystyle 800\)

\(\displaystyle 1551\)

\(\displaystyle 53\)

\(\displaystyle 223\)

Correct answer:

\(\displaystyle 800\)

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 \(\displaystyle A=\begin{vmatrix} 5&-5 &-3 \\-5 &5 &-7 \\7 &9 &5 \end{vmatrix}\)

The determinant is thus:

\(\displaystyle |A|=5[5(5)-9(-7)]-(-5)[-5(5)-7(-7)]+(-3)[-5(9)-7(5)]=800\)

Example Question #692 : Vectors And Vector Operations

Find the determinant of the matrix \(\displaystyle A=\begin{vmatrix} -6& 0& 2\\8 &-8 &-8 \\8 &1 &0 \end{vmatrix}\)

Possible Answers:

\(\displaystyle 96\)

\(\displaystyle 21\)

\(\displaystyle 0\)

\(\displaystyle -255\)

\(\displaystyle -144\)

Correct answer:

\(\displaystyle 96\)

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 \(\displaystyle A=\begin{vmatrix} -6& 0& 2\\8 &-8 &-8 \\8 &1 &0 \end{vmatrix}\)

The determinant is thus:

\(\displaystyle |A|=-6[-8(0)-1(-8)]-0[8(0)-8(-8)]+2[8(1)-8(-8)]=96\)

Example Question #693 : Vectors And Vector Operations

Find the determinant of the matrix \(\displaystyle A=\begin{vmatrix} 8& -2&5 \\ 8& 6& 5\\4 &7 &6 \end{vmatrix}\)

Possible Answers:

\(\displaystyle 224\)

\(\displaystyle 1004\)

\(\displaystyle 488\)

\(\displaystyle 125\)

\(\displaystyle 33\)

Correct answer:

\(\displaystyle 224\)

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 \(\displaystyle A=\begin{vmatrix} 8& -2&5 \\ 8& 6& 5\\4 &7 &6 \end{vmatrix}\)

The determinant is thus:

\(\displaystyle |A|=8[6(6)-7(5)]-(-2)[8(6)-4(5)]+5[8(7)-4(6)]=224\)

Example Question #694 : Vectors And Vector Operations

Find the determinant of the matrix \(\displaystyle A=\begin{vmatrix} 5& 8&-1 \\-2 &7 &-9 \\9 &5 &-1 \end{vmatrix}\)

Possible Answers:

\(\displaystyle -1000\)

\(\displaystyle -401\)

\(\displaystyle -366\)

\(\displaystyle -503\)

\(\displaystyle -11\)

Correct answer:

\(\displaystyle -401\)

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 \(\displaystyle A=\begin{vmatrix} 5& 8&-1 \\-2 &7 &-9 \\9 &5 &-1 \end{vmatrix}\)

The determinant is thus:

\(\displaystyle |A|=5[7(-1)-5(-9)]-8[-2(-1)-9(-9)]+(-1)[-2(5)-9(7)]=-401\)

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