KVPY Sample Paper KVPY Stream-SX Model Paper-12

  • question_answer
    A function \[F(x)\] satisfied the functional equation \[{{x}^{2}}f(x)+F(1-x)=2x-{{x}^{4}}\] for all real \[z,F(x)\] must be

    A) \[{{x}^{2}}\]

    B) \[1-{{x}^{2}}\]

    C) \[1+{{x}^{2}}\]

    D) \[{{x}^{2}}+x+1\]

    Correct Answer: B

    Solution :

    \[{{x}^{2}}F(x)+f(1-x)=2x-{{x}^{4}}\]
    Replacing \[x\] by \[1-x,\] gives \[{{(1-x)}^{2}}F(1-x)+F(x)\]
    \[=2(1-x)-{{(1-x)}^{4}}\]                                  ?(2)
    Multiplying (1) by \[{{\left( 1-x \right)}^{2}}\]and subtracting (2) from it gives \[[{{x}^{2}}{{(1-x)}^{2}}-1]F(x)\]
    \[=2x{{(1-x)}^{2}}-{{x}^{4}}{{(1-x)}^{2}}\]\[-2(1-x)+{{(1-x)}^{4}}\]
    \[\Rightarrow [x(1-x)-1][x(1-x)+1]F(x)\]                  
    \[=2(1-x)[x(1-x)-1]\]\[-{{(1-x)}^{2}}[{{x}^{4}}-{{(1-x)}^{2}}]\]
    \[\Rightarrow \]\[[x-1-{{x}^{2}}][x+1-{{x}^{2}}]F(x)\]
    \[=2(1-x)[x-1-{{x}^{2}}]\]\[-{{(1-x)}^{2}}({{x}^{2}}-1+x)({{x}^{2}}+1-x)\]
    \[\Rightarrow \]\[(x+1-{{x}^{2}})F(x)\]
    \[=(1-x)[2+(1-x)({{x}^{2}}+x-1)]\]
    \[=(1-x)[2+2x-{{x}^{3}}-1]\]
    \[=(1-x)[2(1+x)-(x+1)({{x}^{2}}-x+1)]\]
    \[=(1-{{x}^{2}})[1+x-{{x}^{2}}]\]
    \[\therefore F\left( x \right)=1-{{x}^{2}}\]


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