CET Karnataka Engineering CET - Karnataka Engineering Solved Paper-2003

  • question_answer
    If the distance of any point P from the points \[A\,(a+b,\,\,a-b)\] and B \[B\,(a-b,\,\,a+b)\] are equal then the locus of P is :

    A)  \[ax+by=0\]                     

    B)  \[x-y=0\]

    C)  \[x+y=0\]                          

    D)  \[bx-ay=0\]

    Correct Answer: B

    Solution :

    Let P be \[(x,\text{ }y)\], and we have \[A=(a+b,\,\,a-b),B=(a-b\text{, }a\text{ }+b)\] Here      \[PA=PB\]                 \[P{{A}^{2}}=P{{B}^{2}}\] \[\Rightarrow \] \[{{[x-(a+b)]}^{2}}+{{[y-(a-b)]}^{2}}\]                 \[={{[x-(a-b)]}^{2}}+{{[y-(a+b)]}^{2}}\] \[\Rightarrow \] \[{{[x-(a+b)]}^{2}}-{{[x-(a-b)]}^{2}}\]                 \[={{[y-(a+b)]}^{2}}-{{[y-(a-b)]}^{2}}\] \[\Rightarrow [x-(a+b)+x-(a-b)]\,[x-(a+b)-x+a-b]\]\[\Rightarrow [y-(a+b)+y-(a-b)]\,[y-(a+b)-y+a-b]\]   [Using \[{{x}^{2}}-{{y}^{2}}=(x+y)\,\,(x-y)\]] \[\Rightarrow \]               \[(2x-2a)\,(-2b)=(2y-2a)\,(-2b)\] \[\Rightarrow \]               \[2x-2a=2y-2a\] \[\Rightarrow \]               \[x-y=0\]


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