JEE Main & Advanced Mathematics Complex Numbers and Quadratic Equations Question Bank Relation between roots and coefficients

  • question_answer
    If a root of the equation \[a{{x}^{2}}+bx+c=0\]be reciprocal of a root of the equation  then\[{a}'{{x}^{2}}+{b}'x+{c}'=0\], then [IIT 1968]

    A) \[{{(c{c}'-a{a}')}^{2}}=(b{a}'-c{b}')(a{b}'-b{c}')\]

    B) \[{{(b{b}'-a{a}')}^{2}}=(c{a}'-b{c}')(a{b}'-b{c}')\]

    C) \[{{(c{c}'-a{a}')}^{2}}=(b{a}'+c{b}')(a{b}'+b{c}')\]

    D) None of these

    Correct Answer: A

    Solution :

    Let \[\alpha \]be a root of first equation, then \[\frac{1}{\alpha }\] be a root of second equation. Therefore \[a{{\alpha }^{2}}+b\alpha +c=0\]and \[a'\frac{1}{{{\alpha }^{2}}}+{b}'\frac{1}{\alpha }+{c}'=0\] or \[{c}'{{\alpha }^{2}}+{b}'\alpha +{a}'=0\] Hence \[\frac{{{\alpha }^{2}}}{b{a}'-{b}'c}=\frac{\alpha }{c{c}'-a{a}'}=\frac{1}{a{b}'-b{c}'}\] \[{{(cc'-aa')}^{2}}=(ba'-cb')(ab'-bc')\].


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