Manipal Engineering Manipal Engineering Solved Paper-2009

  • question_answer
    The image of the point (3, 2, 1) in the plane\[2x-y+3z=7\]is

    A)  (1, 2, 3)                               

    B)  (2, 3, 1)

    C)  (3, 2, 1)               

    D)         (2, 1, 3)

    Correct Answer: C

    Solution :

    We know that image\[(x,\,\,y,\,\,z)\]of a point \[({{x}_{1}},\,\,{{y}_{1}},\,\,{{z}_{1}})\]in a plane\[ax+by+cz+d=0\]is                 \[\frac{x-{{x}_{1}}}{a}=\frac{y-{{y}_{1}}}{b}=\frac{z-{{z}_{1}}}{c}\]                 \[=\frac{-2(a{{x}_{1}}+b{{y}_{1}}+c{{z}_{1}}+d)}{{{a}^{2}}+{{b}^{2}}+{{c}^{2}}}\] Here, point is\[(3,\,\,2,\,\,1)\]and plane is\[2x-y+3z=7\]. \[\therefore \]  \[\frac{x-3}{2}=\frac{y-2}{-1}=\frac{z-1}{3}\]                 \[=\frac{-2[2(3)\,-(2)+3(1)-7]}{{{2}^{2}}={{1}^{2}}+{{3}^{2}}}\]                 \[\Rightarrow \,\frac{x-3}{2}=\frac{y-2}{-1}=\frac{z-1}{3}=-2(0)\]                 \[\Rightarrow \,\,x=3,\,y=2,\,z=1\]


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