Question

Let \[A = \left[ {\begin{array}{*{20}{c}} 5&6&1\\ 2&{ - 1}&5 \end{array}} \right].\]    Let there exist a matrix $$B$$ such that \[AB = \,\left[ {\begin{array}{*{20}{c}} {35}&{49}\\ {29}&{13} \end{array}} \right].\]    What is $$B$$ equal to ?

A. \[\left[ {\begin{array}{*{20}{c}} 5&1&4\\ 2&{ 6}&3 \end{array}} \right]\]
B. \[\left[ {\begin{array}{*{20}{c}} 2&6&3\\ 5&{1}&4 \end{array}} \right]\]
C. \[\left[ {\begin{array}{*{20}{c}} 5\\ 1\\ 4 \end{array}\,\,\,\,\,\begin{array}{*{20}{c}} 2\\ 6\\ 3 \end{array}} \right]\]  
D. \[\left[ {\begin{array}{*{20}{c}} 2\\ 6\\ 3 \end{array}\,\,\,\,\,\begin{array}{*{20}{c}} 5\\ 1\\ 4 \end{array}} \right]\]
Answer :   \[\left[ {\begin{array}{*{20}{c}} 5\\ 1\\ 4 \end{array}\,\,\,\,\,\begin{array}{*{20}{c}} 2\\ 6\\ 3 \end{array}} \right]\]
Solution :
\[\begin{array}{l} A = \left[ {\begin{array}{*{20}{c}} 5&6&1\\ 2&{ - 1}&5 \end{array}} \right]\,\,{\rm{and}}\,{\rm{let}}\,\,B = \left[ {\begin{array}{*{20}{c}} 5\\ 1\\ 4 \end{array}\,\,\,\,\,\begin{array}{*{20}{c}} 2\\ 6\\ 3 \end{array}} \right]\\ \therefore \,AB = \left[ {\begin{array}{*{20}{c}} 5&6&1\\ 2&{ - 1}&5 \end{array}} \right]\,\left[ {\begin{array}{*{20}{c}} 5\\ 1\\ 4 \end{array}\,\,\,\,\,\begin{array}{*{20}{c}} 2\\ 6\\ 3 \end{array}} \right]\\ = \,\left[ {\begin{array}{*{20}{c}} {25 + 6 + 4}&{10 + 36 + 3}\\ {10 - 1 + 20}&{4 - 6 + 15} \end{array}} \right]\\ = \,\left[ {\begin{array}{*{20}{c}} {35}&{49}\\ {29}&{13} \end{array}} \right] \end{array}\]

Releted MCQ Question on
Algebra >> Matrices and Determinants

Releted Question 1

Consider the set $$A$$ of all determinants of order 3 with entries 0 or 1 only. Let $$B$$  be the subset of $$A$$ consisting of all determinants with value 1. Let $$C$$  be the subset of $$A$$ consisting of all determinants with value $$- 1.$$ Then

A. $$C$$ is empty
B. $$B$$  has as many elements as $$C$$
C. $$A = B \cup C$$
D. $$B$$  has twice as many elements as elements as $$C$$
Releted Question 2

If $$\omega \left( { \ne 1} \right)$$  is a cube root of unity, then
\[\left| {\begin{array}{*{20}{c}} 1&{1 + i + {\omega ^2}}&{{\omega ^2}}\\ {1 - i}&{ - 1}&{{\omega ^2} - 1}\\ { - i}&{ - i + \omega - 1}&{ - 1} \end{array}} \right|=\]

A. 0
B. 1
C. $$i$$
D. $$\omega $$
Releted Question 3

Let $$a, b, c$$  be the real numbers. Then following system of equations in $$x, y$$  and $$z$$
$$\frac{{{x^2}}}{{{a^2}}} + \frac{{{y^2}}}{{{b^2}}} - \frac{{{z^2}}}{{{c^2}}} = 1,$$    $$\frac{{{x^2}}}{{{a^2}}} - \frac{{{y^2}}}{{{b^2}}} + \frac{{{z^2}}}{{{c^2}}} = 1,$$    $$ - \frac{{{x^2}}}{{{a^2}}} + \frac{{{y^2}}}{{{b^2}}} + \frac{{{z^2}}}{{{c^2}}} = 1$$     has

A. no solution
B. unique solution
C. infinitely many solutions
D. finitely many solutions
Releted Question 4

If $$A$$ and $$B$$ are square matrices of equal degree, then which one is correct among the followings?

A. $$A + B = B + A$$
B. $$A + B = A - B$$
C. $$A - B = B - A$$
D. $$AB=BA$$

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