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If $A_1B_1C_1,\, A_2B_2C_2,\, A_3B_3C_3$ are three digit number each of which is divisible by $k$ and $\Delta = \left| {\begin{array}{*{20}{c}}
{{A_1}{\kern 1pt} }&{{B_1}}&{{C_1}} \\
{{A_2}}&{{B_2}}&{{C_2}} \\
{{A_3}}&{{B_3}}&{{C_3}}
\end{array}} \right|$ ; then $\Delta $ is divisible by
$k$
$k^2$
$k^3$
None
Solution
Let $\mathrm{A}_{1} \mathrm{B}_{1} \mathrm{C}_{1}=100 \mathrm{A}_{1}+10 \mathrm{B}_{1}+\mathrm{C}_{1}=\mathrm{pk}$
$\mathrm{A}_{2} \mathrm{B}_{2} \mathrm{C}_{2}=100 \mathrm{A}_{2}+10 \mathrm{B}_{2}+\mathrm{C}_{2}=\mathrm{q} \mathrm{k}$
$\mathrm{A}_{3} \mathrm{B}_{3} \mathrm{C}_{3}=100 \mathrm{A}_{3}+10 \mathrm{B}_{3}+\mathrm{C}_{3}=\mathrm{rk}\left(\text { where } \mathrm{p}_{1} \mathrm{q}_{1} \mathrm{r} \in \mathrm{I}\right)$
so $\Delta=\mathrm{C}_{3} \rightarrow \mathrm{C}_{3}+100 \mathrm{C}_{1}+10 \mathrm{C}_{2}$
$\Delta=\left|\begin{array}{lll}{\mathrm{A}_{1}} & {\mathrm{B}_{1}} & {\mathrm{pk}} \\ {\mathrm{A}_{2}} & {\mathrm{B}_{2}} & {\mathrm{qk}} \\ {\mathrm{A}_{3}} & {\mathrm{B}_{3}} & {\mathrm{rk}}\end{array}\right|=\mathrm{k} \cdot$ Integes (divisible by $k$ )