CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2010

  • question_answer
    The modulus of the complex number\[z\]such that\[|z+3-i|=1\]and \[arg\,(z)=\pi \] is equal to

    A)  1                                            

    B)  2

    C)  9                            

    D)         4

    E)  3

    Correct Answer: E

    Solution :

    Let\[z=x+iy\] \[\therefore \]  \[|z+3-i|=1\] \[\Rightarrow \]               \[|x+iy+3-i|=1\] \[\Rightarrow \]               \[|x+3+i(y-1)|=1\] \[\Rightarrow \]               \[{{(x+3)}^{2}}+{{(y-1)}^{2}}=1\]                            ...(i) But        \[{{\tan }^{-1}}\frac{y}{x}=\pi \] \[\Rightarrow \]               \[y=0\]                                   ...(ii) \[\therefore \]From Eqs. (i) and (ii), we get \[{{(x+3)}^{2}}=0\] \[\Rightarrow \]               \[x=-3,-3\] \[\therefore \]Required complex number is \[x+iy=-3\] \[\therefore \]  \[|x+iy|=|-3|=3\]


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