Question

If $${A_1}{B_1}{C_1},{A_2}{B_2}{C_2}$$    and $${A_3}{B_3}{C_3}$$  are three digit numbers, each of which is divisible by $$k,$$ then \[\Delta = \left| {\begin{array}{*{20}{c}} {{A_1}}&{{B_1}}&{{C_1}}\\ {{A_2}}&{{B_2}}&{{C_2}}\\ {{A_3}}&{{B_3}}&{{C_3}} \end{array}} \right|\]    is

A. divisible by $$k$$  
B. divisible by $$k^2$$
C. divisible by $$k^3$$
D. None of these
Answer :   divisible by $$k$$
Solution :
Since, $${A_1}{B_1}{C_1},{A_2}{B_2}{C_2}$$    and $${A_3}{B_3}{C_3}$$  are divisible by $$k,$$ therefore; $$100{A_1} + 10{B_1} + {C_1} = {n_1}k;100{A_2} + 10{B_2} + {C_2} = {n_2}k;100{A_3} + 10{B_3} + {C_3} = {n_3}k$$
(where $${n_1} , {n_2} , {n_3}$$  are integers)
Now, \[\Delta = \left| {\begin{array}{*{20}{c}} {{A_1}}&{{B_1}}&{{C_1}}\\ {{A_2}}&{{B_2}}&{{C_2}}\\ {{A_3}}&{{B_3}}&{{C_3}} \end{array}} \right|\]
\[\begin{array}{l} = \left| {\begin{array}{*{20}{c}} {{A_1}}&{{B_1}}&{100{A_1} + 10{B_1} + {C_1}}\\ {{A_2}}&{{B_2}}&{100{A_2} + 10{B_2} + {C_2}}\\ {{A_3}}&{{B_3}}&{100{A_3} + 10{B_3} + {C_3}} \end{array}} \right|\left[ {{\rm{Applying, }}{C_3} \to {C_3} + 10{C_2} + 100{C_1}} \right]\\ = \left| {\begin{array}{*{20}{c}} {{A_1}}&{{B_1}}&{{n_1}k}\\ {{A_2}}&{{B_2}}&{{n_2}k}\\ {{A_3}}&{{B_3}}&{{n_3}k} \end{array}} \right| = k\left| {\begin{array}{*{20}{c}} {{A_1}}&{{B_1}}&{{n_1}}\\ {{A_2}}&{{B_2}}&{{n_2}}\\ {{A_3}}&{{B_3}}&{{n_3}} \end{array}} \right| = k{\Delta _1} \end{array}\]
⇒ $$\Delta$$ is divisible by $$k$$
[Since, elements of $$\Delta_1$$ are integers ∴ $$\Delta_1$$ is an integer.]

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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