JAMIA MILLIA ISLAMIA Jamia Millia Islamia Solved Paper-2009

  • question_answer
        If\[f(x+2y,x,x-2y)=xy,\]then\[f(x,y)\]equals

    A)  \[\frac{{{x}^{2}}-{{y}^{2}}}{8}\]                

    B)  \[\frac{{{x}^{2}}-{{y}^{2}}}{4}\]

    C)  \[\frac{{{x}^{2}}+{{y}^{2}}}{4}\]                               

    D)  \[\frac{{{x}^{2}}-{{y}^{2}}}{2}\]

    Correct Answer: A

    Solution :

                    We have, \[f(x+2y,x-2y)=xy\]       ... (i) Let\[x+2y=u\]and \[x-2y=v\] Then,\[x=\frac{u+v}{2}\]and\[y=\frac{u-v}{4}\] Substituting the values of\[x\]and y in Eq. (i), we obtain \[f(u,v)=\frac{{{u}^{2}}-{{v}^{2}}}{8}\Rightarrow f(x,y)=\frac{{{x}^{2}}-{{y}^{2}}}{8}\]


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