JEE Main & Advanced Sample Paper JEE Main Sample Paper-15

  • question_answer
    If \[\frac{3}{2+{{e}^{i\theta }}}=ax+i\]by, 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 them

    Correct Answer: D

    Solution :

    \[\frac{3}{ax+i\,by}-2={{e}^{i\theta }}\]\[\frac{3-2ax-2iby}{ax+i\,\text{by}}={{e}^{i\theta }}\] 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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