Manipal Engineering Manipal Engineering Solved Paper-2009

  • question_answer
    The midpoint of the chord\[4x-3y=5\]of the hyperbola\[2{{x}^{2}}-3{{y}^{2}}=12\]is

    A) \[\left( 0,\,\,-\frac{5}{3} \right)\]                             

    B) \[(2,\,\,1)\]

    C) \[\left( \frac{5}{4},\,\,0 \right)\]               

    D)        \[\left( \frac{11}{4},\,\,2 \right)\]

    Correct Answer: B

    Solution :

    Given,\[4x-3y=5\]and\[2{{x}^{2}}-3{{y}^{2}}=12\] \[\therefore \]  \[2{{\left( \frac{5+3y}{4} \right)}^{2}}-3{{y}^{2}}=12\] \[\Rightarrow \]\[\frac{(25+9{{y}^{2}}+30y)}{8}-3{{y}^{2}}=12\] \[\Rightarrow \]               \[15{{y}^{2}}-30+71=0\] \[\Rightarrow \]               \[y=\frac{30\pm \sqrt{900-4260}}{30}\]                 \[=1\pm \frac{\sqrt{-3360}}{30}\] Also,      \[2{{x}^{2}}-3{{\left( \frac{4x-5}{3} \right)}^{2}}=12\] \[\Rightarrow \]               \[10{{x}^{2}}-40x+61=0\] \[\Rightarrow \]               \[x=\frac{40\pm \sqrt{1600-4\times 10\times 61}}{2\times 10}\]                 \[=\frac{40\pm \sqrt{-840}}{20}=2\pm \frac{\sqrt{-840}}{20}\] \[\therefore \]Points are\[A\left( 2+\frac{\sqrt{-840}}{20},\,\,1+\frac{\sqrt{-3360}}{30} \right)\]and \[B\left( 2-\frac{\sqrt{-840}}{20},\,\,1-\frac{\sqrt{-3360}}{30} \right)\] \[\therefore \]Midpoint of\[AB\] is (2, 1).


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