Manipal Engineering Manipal Engineering Solved Paper-2012

  • question_answer
    If\[f(x)={{x}^{2}}+2bx+2{{c}^{2}}\]and\[g(x)=-{{x}^{2}}+2cx+{{b}^{2}}\] are such that\[f(x)>\max g(x)\], then relation between\[b\]and \[c\]is

    A)  no relation                        

    B) \[0<c<\frac{b}{2}\]

    C) \[|c|<\sqrt{2}|b|\]       

    D)        \[|c|\,\,>\sqrt{2}|b|\]

    Correct Answer: D

    Solution :

    We have,     \[f(x)={{(x+b)}^{2}}+2{{c}^{2}}-{{b}^{2}}\] \[\Rightarrow \]               \[\min f(x)=2{{c}^{2}}-{{b}^{2}}\] and                \[g(x)={{b}^{2}}+{{c}^{2}}-{{(x+c)}^{2}}\]      \[\Rightarrow \]               \[\max g(x)={{b}^{2}}+{{c}^{2}}\] Thus,     \[\max f(x)>\max g(x)\] \[\Rightarrow \]               \[2{{c}^{2}}-{{b}^{2}}>{{b}^{2}}+{{c}^{2}}\] \[\Rightarrow \]               \[{{c}^{2}}>2{{b}^{2}}\]  \[\Rightarrow \]  \[|c|\,\,>\sqrt{2}|b|\]


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