RAJASTHAN ­ PET Rajasthan PET Solved Paper-2009

  • question_answer
    If\[f(x)=\left| \begin{matrix}    1+a & 1-ax & 1+a{{x}^{2}}  \\    1+b & 1+bx & 1+b{{x}^{2}}  \\    1+c & 1+cx & 1+c{{x}^{2}}  \\ \end{matrix} \right|,\]where\[a,b,c\] are non-zero Constants, then value of\[f(10)\] is

    A)  \[10(b-a)(c-a)\]

    B)  \[100(b-a)(c-b)(a-c)\]

    C)  \[100\,abc\]

    D)  0

    Correct Answer: D

    Solution :

     \[f(x)=\left| \begin{matrix}    1+a & 1+ax & 1+a{{x}^{2}}  \\    1+b & 1+bx & 1+b{{x}^{2}}  \\    1+c & 1+cx & 1+c{{x}^{2}}  \\ \end{matrix} \right|\] Applying\[{{C}_{2}}\to {{C}_{2}}-{{C}_{1}}\]and\[{{C}_{3}}\to {{C}_{3}}-{{C}_{2}}\] \[\Rightarrow \]\[f(x)=\left| \begin{matrix}    1+a & a(x-1) & ax(x-1)  \\    1+b & b(x-1) & dx(x-1)  \\    1+c & c(x-1) & cx(x-1)  \\ \end{matrix} \right|\] \[=(x-1)x(x-1)\left| \begin{matrix}    1+a & a & a  \\    1+b & b & b  \\    1+c & c & c  \\ \end{matrix} \right|\] (\[\because \]Two columns are same.) =0


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