J & K CET Engineering J and K - CET Engineering Solved Paper-2012

  • question_answer
    If the points \[(2a,\,a),\,(a,\,2a)\] and \[(a,\,\,a)\] form a triangle of area \[32\text{ }sq\]units, then the centroid of the triangle is

    A)  \[(32,\,\,32)\]        

    B)  \[(-32,\,\,-32)\]

    C)  \[(3,\,3)\]

    D)  \[\left( \frac{32}{3},\,\frac{32}{3} \right)\]

    Correct Answer: D

    Solution :

    \[\because \] Area of triangle, \[=\frac{1}{2}\left\| \begin{matrix}    {{x}_{1}} & {{y}_{1}} & 1  \\    {{x}_{2}} & {{y}_{2}} & 1  \\    {{x}_{3}} & {{y}_{3}} & 1  \\ \end{matrix} \right\|\] \[\therefore \] \[32=\frac{1}{2}\left\| \begin{matrix}    2a & a & 1  \\    a & 2a & 1  \\    a & a & 1  \\ \end{matrix} \right\|\] \[\Rightarrow \] \[64={{a}^{2}}\left\| \begin{matrix}    2 & 1 & 1  \\    1 & 2 & 1  \\    1 & 1 & 1  \\ \end{matrix} \right\|\] \[\Rightarrow \]  \[64={{a}^{2}}|2(2-1)-1(1-1)+1(1-2)|\] \[\Rightarrow \] \[64={{a}^{2}}|2-0-1|={{a}^{2}}\] \[\Rightarrow \] \[a=\pm 8\] \[\therefore \] The given points becomes. \[(\pm \,\,16,\,\pm 8),\,(\pm \,\,8,\,\,\pm 16)\] and \[(\pm \,\,8,\,\,\pm 8)\]. \[\therefore \]   Centroid \[=\left[ \pm \frac{(16+8+8)}{3},\pm \frac{(8+16+8)}{3} \right]\] \[=\left( \pm \frac{32}{3},\pm \frac{32}{3} \right)\]


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