JEE Main & Advanced Sample Paper JEE Main - Mock Test - 42

  • question_answer
    \[\left| {{Z}_{1}}+{{Z}_{2}} \right|=\left| {{Z}_{1}} \right|+\left| {{Z}_{2}} \right|\] is possible if -

    A) \[{{z}_{2}}=1\]              

    B)        \[{{z}_{2}}=\frac{1}{{{z}_{1}}}\]

    C) \[arg\left( {{z}_{1}} \right)=arg\left( {{z}_{2}} \right)\]

    D)        \[\left| {{z}_{1}} \right|=\left| {{z}_{2}} \right|\]

    Correct Answer: C

    Solution :

    [c] \[|{{z}_{1}}+{{z}_{2}}{{|}^{2}}={{(\left| {{z}_{1}} \right|+\left| {{z}_{2}} \right|)}^{2}}\] \[{{\left| {{Z}_{1}} \right|}^{2}}+{{\left| {{Z}_{2}} \right|}^{2}}+2\left| {{Z}_{1}} \right|\left| {{Z}_{2}} \right|COS\left( {{\theta }_{1}}-{{\theta }_{1}} \right)={{\left| {{Z}_{1}} \right|}^{2}}+{{\left| {{Z}_{2}} \right|}^{2}}2\left| {{z}_{1}} \right|\left| {{z}_{2}} \right|\]\[cos\left( {{\theta }_{1}}-{{\theta }_{2}} \right)=1\] \[{{\theta }_{1}}-{{\theta }_{2}}=0{}^\circ \] \[Arg({{z}_{1}})=Arg({{z}_{2}})\]


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