JEE Main & Advanced Sample Paper JEE Main Sample Paper-18

  • question_answer
    Given\[\frac{x}{a}+\frac{y}{b}=1\]and\[ax+by=1\]are two variable lines, \['a'\] and \['b'\] being the parameters connected by the relation\[{{a}^{2}}+{{b}^{2}}=ab\]. The locus of the point of intersection has the equation

    A)  \[{{x}^{2}}+{{y}^{2}}+xy-1=0\]

    B)  \[{{x}^{2}}+{{y}^{2}}-xy+1=0\]

    C)  \[{{x}^{2}}+{{y}^{2}}+xy+1=0\]

    D)  \[{{x}^{2}}+{{y}^{2}}-xy-1=0\]

    Correct Answer: A

    Solution :

     Let (h, k) be point of intersection then \[\frac{h}{a}+\frac{k}{b}=1\] and \[ah+bk=1\] Also, it is given that\[{{a}^{2}}+{{b}^{2}}=1\]. Multiplying (i) and (ii), we get \[{{h}^{2}}+{{k}^{2}}+hk\left( \frac{b}{a}+\frac{a}{b} \right)=1\] or            \[{{h}^{2}}+{{k}^{2}}+hk=1\] or            \[{{x}^{2}}+{{y}^{2}}+xy-1=0\]


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