JEE Main & Advanced Sample Paper JEE Main Sample Paper-29

  • question_answer
    If \[\frac{3}{2+{{e}^{i\theta }}}=ax+iby\], (where \[\theta \] is parameter) then the locus of \[P(x,y)\] will represent

    A) ellipse if \[a=1,\,b=2\]

    B) circle if \[a=\,b=1\]

    C) pair of straight line if \[a=\,1,b=0\]

    D) all of above

    Correct Answer: D

    Solution :

    \[\frac{3}{ax+iby}-2={{e}^{i\theta }}\] \[\frac{3-2ax-2iby}{ax+iby}={{e}^{i\theta }}\]                 Take modulus both sides                 \[{{(3-2ax)}^{2}}+4{{b}^{2}}{{y}^{2}}={{a}^{2}}{{x}^{2}}+{{b}^{2}}{{y}^{2}}\]                 When \[a=1\]and \[b=2\]then \[\frac{{{(x-2)}^{2}}}{1}+\frac{{{y}^{2}}}{1/4}=1\]                 which is an ellipse                 When \[a=b=1\] then circle. When \[a=1\]and \[b=2\] then \[{{x}^{2}}+4x+3=0\]represent pair of straight line.         


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