Matrices

Show that
$\begin{array}{l} \cos \theta \cdot\left[\begin{array}{cc} \cos \theta & \sin \theta \\ -\sin \theta & \cos \theta \end{array}\right]+\sin \theta \\ {\left[\begin{array}{cc} \sin \theta & -\cos \theta \\ \cos \theta & \sin \theta \end{array}\right]=I} \end{array}$

Solution: We have $\cos \theta\left(\begin{array}{cc}\cos \theta & \sin \theta \\ -\sin \theta & \cos \theta\end{array}\right)+\sin \theta\left(\begin{array}{cc}\sin \theta & -\cos...

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For each of the following pairs of matrices $A$ and $B$, verify that $(A B)^{\prime}=\left(B^{\prime} A^{\prime}\right)$ : $A=\left[\begin{array}{rrr}-1 & 2 & -3 \\ 4 & -5 & 6\end{array}\right]$ and $B=\left[\begin{array}{cc}3 & -4 \\ 2 & 1 \\ -1 & 0\end{array}\right]$

Solution: Take $\mathrm{C}=\mathrm{AB}$ $\begin{array}{l} C=\left[\begin{array}{ccc} -1 & 2 & -3 \\ 4 & -5 & 6 \end{array}\right]\left[\begin{array}{cc} 3 & -4 \\ 2 & 1 \\ -1...

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For each of the following pairs of matrices $A$ and $B$, verify that $(A B)^{\prime}=\left(B^{\prime} A^{\prime}\right)$ : $A=\left[\begin{array}{ll} 1 & 3 \\ 2 & 4 \end{array}\right] \text { and } B=\left[\begin{array}{ll} 1 & 4 \\ 2 & 5 \end{array}\right]$

Solution: Take $\mathrm{C}=\mathrm{A} 8$ $\begin{array}{l} C=\left[\begin{array}{ll} 1 & 3 \\ 2 & 4 \end{array}\right]\left[\begin{array}{ll} 1 & 4 \\ 2 & 5 \end{array}\right] \\...

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If $A=\left[\begin{array}{ccc}1 & 0 & -2 \\ 3 & -1 & 0 \\ -2 & 1 & 1\end{array}\right], B=\left[\begin{array}{ccc}0 & 5 & -4 \\ -2 & 1 & 3 \\ 1 & 0 & 2\end{array}\right]$ and $C=\left[\begin{array}{ccc}1 & 5 & 2 \\ -1 & 1 & 0 \\ 0 & -1 & 1\end{array}\right] ;$ verify that $A(B-C)=(A B-A C)$

Solution: We have $A=\left(\begin{array}{ccc}1 & 0 & 2 \\ 3 & -1 & 0 \\ -2 & 1 & 1\end{array}\right), B=\left(\begin{array}{ccc}0 & 5 & -4 \\ -2 & 1 & 3 \\ 1...

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Verify that $A(B+C)=(A B+A C)$, when $\mathrm{A}=\left[\begin{array}{ll} 1 & 2 \\ 3 & 4 \end{array}\right], \mathrm{B}=\left[\begin{array}{cc} 2 & 0 \\ 1 & -3 \end{array}\right] \text { and } \mathrm{C}=\left[\begin{array}{cc} 1 & -1 \\ 0 & 1 \end{array}\right]$

Solution: We have $\boldsymbol{A}=\left(\begin{array}{ll}\mathbf{1} & \mathbf{2} \\ \mathbf{3} & \mathbf{4}\end{array}\right), \boldsymbol{B}=\left(\begin{array}{cc}\mathbf{2} &...

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For the following matrices, verify that $A(B C)=(A B) C$ : $\mathrm{A}=\left[\begin{array}{ccc} 2 & 3 & -1 \\ 3 & 0 & 2 \end{array}\right], \mathrm{B}=\left[\begin{array}{l} 1 \\ 1 \\ 2 \end{array}\right] \text { and } \mathrm{C}=\left[\begin{array}{ll} 1 & -2 \end{array}\right]$

Solution: We have $\boldsymbol{A}=\left(\begin{array}{ccc}\mathbf{2} & \mathbf{3} & \mathbf{- 1} \\ \mathbf{3} & \mathbf{0} & \mathbf{2}\end{array}\right),...

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For the following matrices, verify that $A(B C)=(A B) C$ : $\mathrm{A}=\left[\begin{array}{lll} 1 & 2 & 5 \\ 0 & 1 & 3 \end{array}\right], \mathrm{B}=\left[\begin{array}{lll} 2 & 3 & 0 \\ 1 & 0 & 4 \\ 1 & -1 & 2 \end{array}\right] \text { and } \mathrm{C}=\left[\begin{array}{l} 1 \\ 4 \\ 5 \end{array}\right]$

Solution: We have $A=\left(\begin{array}{lll}1 & 2 & 5 \\ 0 & 1 & 3\end{array}\right), B=\left(\begin{array}{ccc}2 & 3 & 0 \\ 1 & 0 & 4 \\ 1 & -1 &...

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$\text { If } A=\left[\begin{array}{ccc} 2 & -3 & -5 \\ -1 & 4 & 5 \\ 1 & -3 & -4 \end{array}\right] \text { and } B=\left[\begin{array}{ccc} 2 & -2 & -4 \\ -1 & 3 & 4 \\ 1 & -2 & -3 \end{array}\right] \text {, shown that } A B=A \text { and } B A=B \text {. }$

Solution: We have $\boldsymbol{A}=\left(\begin{array}{ccc}\mathbf{2} & -\mathbf{3} & -\mathbf{5} \\ -\mathbf{1} & \mathbf{4} & \mathbf{5} \\ \mathbf{1} & -\mathbf{3} &...

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Show that $A B=B A$ in each of the following cases: $A=\left[\begin{array}{cc} \cos \theta & -\sin \theta \\ \sin \theta & \cos \theta \end{array}\right] \text { and } B=\left[\begin{array}{cc} \cos \phi & -\sin \phi \\ \sin \phi & \cos \phi \end{array}\right]$

Solution: We have $A=\left(\begin{array}{cc}\cos \theta & -\sin \theta \\ \sin \theta & \cos \theta\end{array}\right)$ and $B=\left(\begin{array}{cc}\cos \phi & -\sin \phi \\ \sin \phi...

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Find the value of $x$ and $y$, when
i. $\left[\begin{array}{l}\mathrm{x}+\mathrm{y} \\ \mathrm{x}-\mathrm{y}\end{array}\right]=\left[\begin{array}{l}8 \\ 4\end{array}\right]$
ii. $\left[\begin{array}{cc}2 x+5 & 7 \\ 0 & 3 y-7\end{array}\right]=\left[\begin{array}{cc}x-3 & 7 \\ 0 & -5\end{array}\right]$

Solution: (i) Given $\left(\begin{array}{l}\boldsymbol{x}+\boldsymbol{y} \\ \boldsymbol{x}-\boldsymbol{y}\end{array}\right)=\left(\begin{array}{l}8 \\ \mathbf{4}\end{array}\right)$. By equality of...

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