JCECE Engineering JCECE Engineering Solved Paper-2012

  • question_answer
    The sum of the roots of quadratic equation \[a{{x}^{2}}+bx+c=0(a,\,\,b,\,\,c\ne 0)\] is equal to the sum of squares of their reciprocals, then \[\frac{a}{c},\,\,\frac{b}{a}\] and \[\frac{c}{b}\]are in

    A) \[AP\]                                  

    B) \[GP\]

    C) \[HP\]                                  

    D)  None of these

    Correct Answer: C

    Solution :

    Given, equation is                 \[a{{x}^{2}}+bx+c=0\] If \[\alpha \] and \[\beta \] be the roots of this equation. Then, according to question                 \[\alpha +\beta =\frac{1}{{{\alpha }^{2}}}+\frac{1}{{{\beta }^{2}}}=\frac{{{\alpha }^{2}}+{{\beta }^{2}}}{{{\alpha }^{2}}{{\beta }^{2}}}\]                 \[=\frac{{{(\alpha +\beta )}^{2}}-2\alpha \beta }{{{\alpha }^{2}}{{\beta }^{2}}}\] \[\Rightarrow \]               \[\frac{-b}{a}=\frac{\frac{{{b}^{2}}}{{{a}^{2}}}-2\frac{c}{a}}{\frac{{{c}^{2}}}{{{a}^{2}}}}\] \[\Rightarrow \]               \[\frac{-b}{a}=\frac{{{b}^{2}}-2ac}{{{c}^{2}}}\] \[\Rightarrow \]                \[\frac{2a}{c}=\frac{{{b}^{2}}}{{{c}^{2}}}+\frac{b}{a}=\frac{a{{b}^{2}}+b{{c}^{2}}}{a{{c}^{2}}}\] \[\Rightarrow \]               \[2{{a}^{2}}c=a{{b}^{2}}+b{{c}^{2}}\] \[\Rightarrow \]               \[\frac{2a}{b}=\frac{b}{c}+\frac{c}{a}\] \[\Rightarrow \]               \[\frac{c}{a},\,\,\,\frac{a}{b}\]and\[\frac{b}{c}\]are in\[AP\]. \[\Rightarrow \]               \[\frac{a}{c},\,\,\,\frac{b}{a}\]and\[\frac{c}{b}\]are in\[HP\].


You need to login to perform this action.
You will be redirected in 3 sec spinner