J & K CET Engineering J and K - CET Engineering Solved Paper-2010

  • question_answer
    If \[\left| \begin{matrix}    {{a}_{1}} & {{b}_{1}} & {{c}_{1}}  \\    {{a}_{2}} & {{b}_{2}} & {{c}_{2}}  \\    {{a}_{3}} & {{b}_{3}} & {{c}_{3}}  \\ \end{matrix} \right|=3,\] then \[\left| \begin{matrix}    3\,{{a}_{1}} & 9\,{{b}_{1}} & 3\,{{c}_{1}}  \\    {{a}_{2}} & 3\,{{b}_{2}} & {{c}_{2}}  \\    3\,{{a}_{3}} & 9\,{{b}_{3}} & 3\,{{c}_{3}}  \\ \end{matrix} \right|\] is equal to

    A)  \[51\]             

    B)  \[27\]

    C)  \[81\]               

    D)  \[91\]

    Correct Answer: C

    Solution :

    Given,   \[\left| \begin{matrix}    {{a}_{1}} & {{b}_{1}} & {{c}_{1}}  \\    {{a}_{2}} & {{b}_{2}} & {{c}_{2}}  \\    {{a}_{3}} & {{b}_{3}} & {{c}_{3}}  \\ \end{matrix} \right|=3\] Now, \[\left| \begin{matrix}    3{{a}_{1}} & 9{{b}_{1}} & 3{{c}_{1}}  \\    {{a}_{2}} & 3{{b}_{2}} & {{c}_{2}}  \\    3{{a}_{3}} & 9{{b}_{3}} & 3{{c}_{3}}  \\ \end{matrix} \right|\] \[=3\times 3\left| \begin{matrix}    {{a}_{1}} & 3{{b}_{1}} & {{c}_{1}}  \\    {{a}_{2}} & 3{{b}_{2}} & {{c}_{2}}  \\    {{a}_{3}} & 3{{b}_{3}} & {{c}_{3}}  \\ \end{matrix} \right|\] \[=9\times 3\left| \begin{matrix}    {{a}_{1}} & {{b}_{1}} & {{c}_{1}}  \\    {{a}_{2}} & {{b}_{2}} & {{c}_{2}}  \\    {{a}_{3}} & {{b}_{3}} & {{c}_{3}}  \\ \end{matrix} \right|\] \[=27\times 3=81\]


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