RAJASTHAN ­ PET Rajasthan PET Solved Paper-2002

  • question_answer
    Determinant\[\left| \begin{matrix}    1 & a & {{a}^{2}}-bc  \\    1 & b & {{b}^{2}}-ac  \\    1 & c & {{c}^{2}}-ab  \\ \end{matrix} \right|\]is equal to

    A)  \[a+b+c\]

    B)  \[{{a}^{2}}+{{b}^{2}}+{{c}^{2}}\]

    C)  0

    D)  1

    Correct Answer: C

    Solution :

     \[\left| \begin{matrix}    1 & a & {{a}^{2}}-bc  \\    1 & b & {{b}^{2}}-ac  \\    1 & c & {{c}^{2}}-ab  \\ \end{matrix} \right|\] \[=\left| \begin{matrix}    1 & a & {{a}^{2}}-bc  \\    0 & b-a & {{b}^{2}}-ac-{{a}^{2}}+bc  \\    0 & c-a & {{c}^{2}}-ab-{{a}^{2}}+bc  \\ \end{matrix} \right|\] \[[{{R}_{2}}\to {{R}_{2}}-{{R}_{1}},{{R}_{3}}\to {{R}_{3}}-{{R}_{1}}]\] \[=1[(b-a)({{c}^{2}}-ab-{{a}^{2}}+bc)-(c-a)\] \[({{b}^{2}}-ac-{{a}^{2}}+bc)]\] \[=b{{c}^{2}}-a{{b}^{2}}-{{a}^{2}}b+{{b}^{2}}c-a{{c}^{2}}+{{a}^{2}}b\] \[+{{a}^{3}}-abc-{{b}^{2}}c+a{{c}^{2}}+{{a}^{2}}c-b{{c}^{2}}+a{{b}^{2}}\] \[-{{a}^{2}}c-{{a}^{3}}+abc\] \[=0\]


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