Manipal Engineering Manipal Engineering Solved Paper-2009

  • question_answer
    The area (in square unit) of the triangle formed by\[x+y+1=0\]and the pair of straight lines\[{{x}^{2}}-3xy+2{{y}^{2}}=0\]is

    A) \[\frac{7}{12}\]                                

    B) \[\frac{5}{12}\]

    C) \[\frac{1}{12}\]                

    D)        \[\frac{1}{6}\]

    Correct Answer: C

    Solution :

    Given,\[{{x}^{2}}-2xy-xy+2{{y}^{2}}=0\] \[\Rightarrow \]               \[(x-2y)(x-y)=0\] \[\Rightarrow \]               \[x=2y,\,\,x=y\]                                                ? (i) Also       \[x+y+1=0\]                                       ... (ii) On solving Eqs. (i) and (ii), we get                 \[A\left( -\frac{2}{3},\,\,-\frac{1}{3} \right),\,\,B\left( -\frac{1}{2},\,\,-\frac{1}{2} \right),\,\,C(0,\,\,0)\] \[\therefore \]Area of\[\Delta ABC=\frac{1}{2}\left| \begin{matrix}    -\frac{2}{3} & -\frac{1}{3} & 1  \\    -\frac{1}{2} & -\frac{1}{2} & 0  \\    0 & 0 & 1  \\ \end{matrix} \right|\]                                 \[=\frac{1}{2}\left[ \frac{1}{3}-\frac{1}{6} \right]=\frac{1}{2}\left[ \frac{1}{6} \right]=\frac{1}{12}\]


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