Question

If \[{\vartriangle _1} = \left| {\begin{array}{*{20}{c}} {10}&4&3 \\ {17}&7&4 \\ 4&{ - 5}&7 \end{array}} \right|,{\vartriangle _2} = \left| {\begin{array}{*{20}{c}} 4&{x + 5}&3 \\ 7&{x + 12}&4 \\ { - 5}&{x - 1}&7 \end{array}} \right|\]         such that $${\vartriangle _1} + {\vartriangle _2} = 0$$   then

A. $$x = 5$$  
B. $$x$$ has no real value
C. $$x = 0$$
D. None of these
Answer :   $$x = 5$$
Solution :
\[\begin{array}{l} {\rm{Given,\, }}{\Delta _1} = \left| {\begin{array}{*{20}{c}} {10}&4&3\\ {17}&7&4\\ 4&{ - 5}&7 \end{array}} \right|\\ {C_1} \leftrightarrow {C_2}\\ {\Delta _1} = - \left| {\begin{array}{*{20}{c}} 4&{10}&3\\ 7&{17}&4\\ { - 5}&4&7 \end{array}} \right|\\ {\rm{Also\, given\, }}{\Delta _1} + {\Delta _2} = 0\\ \Rightarrow - \left| {\begin{array}{*{20}{c}} 4&{10}&3\\ 7&{17}&4\\ { - 5}&4&7 \end{array}} \right| + \left| {\begin{array}{*{20}{c}} 4&{x + 5}&3\\ 7&{x + 12}&4\\ { - 5}&{x - 1}&7 \end{array}} \right| = 0\\ \Rightarrow \left| {\begin{array}{*{20}{c}} 4&{x - 5}&3\\ 7&{x - 5}&4\\ { - 5}&{x - 5}&7 \end{array}} \right| = 0\\ \Rightarrow \left( {x - 5} \right)\left| {\begin{array}{*{20}{c}} 4&1&3\\ 7&1&4\\ { - 5}&1&7 \end{array}} \right| = 0\\ \Rightarrow \left( {x - 5} \right)\left( { - 21} \right) = 0\\ \Rightarrow x - 5 = 0\\ \Rightarrow x = 5 \end{array}\]

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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Matrices and Determinants


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