Railways Sample Paper RRBs Assistant Loco Pilot and Technician CBT STAGE-I Sample Paper-25

  • question_answer
    If\[x+y+z=0,\] then\[({{x}^{2}}+xy+{{y}^{2}})\]is equal to

    A)  \[({{y}^{2}}+yx+{{z}^{2}})\]

    B)  \[({{y}^{2}}-yz+{{z}^{2}})\]

    C)  \[({{z}^{2}}-zx+{{x}^{2}})\]

    D)         \[({{z}^{2}}+zx+{{x}^{2}})\]

    Correct Answer: D

    Solution :

    \[x+y+z=0\] \[\Rightarrow \,\] \[\left( x+y \right)=-z\Rightarrow {{\left( x+y \right)}^{2}}={{z}^{2}}\] \[\Rightarrow \,\]\[{{x}^{2}}+{{y}^{2}}+2xy={{z}^{2}}\] \[\Rightarrow \,\]\[{{x}^{2}}+{{y}^{2}}+xy={{z}^{2}}-xy\] \[\,[\therefore x+y+z=0\Rightarrow y=(-x-z)]\] \[={{z}^{2}}-x(-x-z)\] \[\Rightarrow \,\] \[{{x}^{2}}+{{y}^{2}}+xy={{z}^{2}}+zx+{{x}^{2}}\]


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