JEE Main & Advanced JEE Main Paper (Held On 19 April 2014)

  • question_answer
    For all complex numbers z of the form \[1+i\alpha ,\alpha \in R,\]if \[{{z}^{2}}=x+iy,\]then     JEE Main Online Paper (Held On 19 April 2016)

    A) \[{{y}^{2}}-4x+2=0\]      

    B) \[{{y}^{2}}+4x-4=0\]

    C) \[{{y}^{2}}-4x-4=0\]       

    D) \[{{y}^{2}}+4x+2=0\]

    Correct Answer: B

    Solution :

    Let \[z=1+i\alpha ,\alpha \in R\] \[{{z}^{2}}=(1+i\alpha )(1+i\alpha )\] \[x+iy=(1+2i\alpha -{{\alpha }^{2}})\] On comparing real and imaginary parts, we get                 \[x=1-{{\alpha }^{2}},y=2\alpha \] Now, consider option (b), which is \[{{y}^{2}}+4x-4=0\] LHS : \[{{y}^{2}}+4x-4={{(2\alpha )}^{2}}+4(1-{{\alpha }^{2}})-4\] \[=4{{\alpha }^{2}}+4-4{{\alpha }^{2}}-4\] = 0 = R.H.S. Hence, \[{{y}^{2}}+4x-4=0\]


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