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Practice: Determinant of $3\times3$ Matrix

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Wize University Linear Algebra Textbook > Determinants

Determinants and Inverse

3 Activities

Wize University Linear Algebra Textbook > Determinants

(Optional) Shortcut for 3x3 Determinants

3 Activities

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Let A=[61aa−20012]A=\left[\begin{array}{rrr} 6&1&a\\ a&-2&0\\ 0&1&2 \end{array}\right] using cofactor expansion along any row or column

Find the value(s) of aa that will make AA invertible
More Determinants and Inverse Questions:
Practice Question: Determinant Properties
True or False?
If 𝐴 is a 4 × 4 matrix and det(𝐴) = −3, then the homogeneous system of linear equations 𝐴𝑥⃗=0⃗𝐴𝑥⃗=\vec{0} has at least one non-trivial solution.
For what value of d, the following linear system has at least one solution:
{𝑥+𝑦+𝑧=0−𝑥+𝑧=1𝑥+3𝑧=𝑑\begin{cases} 𝑥 + 𝑦 + 𝑧 = 0\\ −𝑥 + 𝑧 = 1\\ 𝑥 + 3𝑧 = 𝑑 \end{cases}
133 - FML 3 - 18.1W e.g. 17.2
If   ⁣A‾\bcb{\boldsymbol{ \ul{A} }} is a 3×3\bcb{\boldsymbol{ 3 \times 3}} matrix with det(  ⁣A‾)=−4\bcb{\boldsymbol{ \det{\ul{A}} = -4}}, find:
det((2A)−1)\boldsymbol{ \det{(2A)^{-1}}}
133 - FML 3 - 18.1W e.g. 15
  ⁣A‾2=4  ⁣A‾ and   ⁣A‾\bcb{\boldsymbol{ \ul{A}^2 = 4\ul{A} \text{ and } \ul{A} }} is an invertible matrix, then a possible value for det(  ⁣A‾)\bcb{\boldsymbol{\det{\ul{A}}}} is:
133 - FML 3 - 18.1W e.g. 69
Given   ⁣A‾ and   ⁣B‾ 3×3\bcb{\boldsymbol{ \ul{A} \text{ and } \ul{B} ~ 3 \times 3}} matrices with det(  ⁣A‾)=−4 and det(BT)=3\bcb{\boldsymbol{\det{\ul{A}} = -4 \text{ and } \det{ \mtran{B} } = 3}} find det(2  ⁣A‾ BT   ⁣A‾−2  ⁣B‾ AT B−1)\bcb{\boldsymbol{ \det { 2\ul{A} \, \mtran{B} \, \ul{A}^{-2} \ul{B} \, \mtran{A} \, \minv{B} } }}
.
133 - FML 3 - 18.1W e.g. 63
  ⁣A‾\bcb{\boldsymbol{ \ul{A} }} is a 3×3\bcb{\boldsymbol{ 3 \times 3}} matrix such that det(−2(AT)−1)=8 then det(  ⁣A‾)\bcb{\boldsymbol{ \det{-2(\mtran{A})^{-1} }= 8 \text{ then } \det{\ul{A}}}} is:
Shortcut for 3x3 Determinants
Let A=[−61aa−2001−2]A=\left[\begin{array}{rrr} -6&1& a\\ a&-2&0\\ 0&1& -2 \end{array}\right]. Find the value(s) of aa such that AA is not invertible.
Let B=[𝑎𝑏𝑐𝑑𝑒𝑓𝑔h𝑖]B=\begin{bmatrix} 𝑎&𝑏&𝑐\\ 𝑑&𝑒&𝑓\\ 𝑔&ℎ&𝑖 \end{bmatrix} be a 3×33\times3 matrix. Assume that det(B)=20\det B = 20. Determine if the matrix A that appears below is invertible by computing its determinant.
A=[5𝑎5𝑏05𝑐0010−𝑔−h0−i𝑑−10𝑎𝑒−10𝑏0𝑓−10𝑐]A=\begin{bmatrix} 5𝑎&5𝑏&0&5𝑐\\ 0&0&1&0\\ −𝑔&-h&0&-i\\ 𝑑 − 10𝑎&𝑒 − 10𝑏&0&𝑓 − 10𝑐 \end{bmatrix}
Let B=[𝑎𝑏𝑐𝑑𝑒𝑓𝑔h𝑖]be a 3X3 matrix. Assume that det(B)=20.Let\ B=\begin{bmatrix} 𝑎&𝑏&𝑐\\ 𝑑&𝑒&𝑓\\ 𝑔&ℎ&𝑖 \end{bmatrix}be\ a\ 3X3\ matrix.\ Assume\ that\ det(B) = 20.
Determine if the matrix A that appears below is invertible by computing its determinant.
Practice: Determinant Properties
Practice: Determinant Properties
True or False?
If 𝐴 is a 4 × 4 matrix and det(𝐴) = −3, then det(AT)=1det(A−1)det\left(A^T\right)=\frac{1}{det\left(A^{-1}\right)}
Determinants and Inverses
Let A=[abcdef12−3]A=\begin{bmatrix} a&b&c\\ d&e&f\\ 1&2&-3 \end{bmatrix}, where it is known that det[abde]=5\text{det}\begin{bmatrix} a&b\\d&e \end{bmatrix}=5, det[acdf]=−2\text{det}\begin{bmatrix} a&c\\d&f \end{bmatrix}=-2 and det[bcef]=3\text{det}\begin{bmatrix} b&c\\e&f \end{bmatrix}=3.
(a) Find detA\text{det}A.
(b) Find the (2,3)-entry of AdjA\text{Adj}A.
Cramer's Rule for Solving Linear Systems: Determinants and Inverses
Let AA be a 3 x 3 matrix with detA=−18\text{det}A=-18 and Adj A=[−9340−6−2006]\text{Adj}\ A= \begin{bmatrix} -9&3&4\\ 0&-6&-2\\ 0&0&6 \end{bmatrix}
(a) Find A−1A^{-1}.
(b) Find the solution to Ax=bA\bm{x}=\bm{b}, where x=[xyz]\bm{x}=\begin{bmatrix} x\\y\\z \end{bmatrix} and b=[−120]\bm{b}=\begin{bmatrix} -1\\2\\0 \end{bmatrix}
Determinants and Inverses
Find the value(s) of kk such that the matrix [10−2123k04]\begin{bmatrix} 1&0&-2\\ 1&2&3\\ k&0&4 \end{bmatrix} has no inverse.
Determinants: Basics
If A=[1234021−500−30000−1]A= \begin{bmatrix} 1&2&3&4\\ 0&2&1&-5\\ 0&0&-3&0\\ 0&0&0&-1 \end{bmatrix}, calculate det(Adj A)det(Adj\ A).
More (Optional) Shortcut for 3x3 Determinants Questions:
133 - FML 3 - 18.1W e.g. 71
  ⁣B‾=  [1234−112x2]\bcb{\boldsymbol{ \ul{B} =  \begin{bmatrix} 1 & 2 & 3 \\ 4 & -1 & 1 \\ 2 & x & 2 \end{bmatrix} }} such that det(  ⁣B‾)=−8 \bcb{\boldsymbol{ \det {\ul{B}} = -8 }} , then x\bcb{\boldsymbol{ x }} is:
(a)  111(b)  −1(c)  0(d)  None of the above\text{(a)}\;\boldsymbol{ \frac{1}{11} } \qquad\qquad\qquad \text{(b)}\; \boldsymbol{ -1}\qquad\qquad\qquad \text{(c)}\; \boldsymbol{ 0}\qquad\qquad\qquad \text{(d)}\; \text{\bf{None of the above}}
Shortcut for 3x3 Determinants
Let A=[−61aa−2001−2]A=\left[\begin{array}{rrr} -6&1& a\\ a&-2&0\\ 0&1& -2 \end{array}\right]. Find the value(s) of aa such that AA is not invertible.
Determinants of Large Matrices
B=[40151002−2]B= \begin{bmatrix} 4&0&1\\ 5&1&0\\ 0&2&-2 \end{bmatrix}
Find det(B)\det B.
Practice: Determinant
Practice Question: Determinant
Find the determinant of [40151002−2]\begin{bmatrix} 4&0&1\\ 5&1&0\\ 0&2&-2 \end{bmatrix}.
Practice: Determinant
Practice: Determinant
Find the determinant of [40151002−2]\begin{bmatrix} 4&0&1\\ 5&1&0\\ 0&2&-2 \end{bmatrix}.