If $\left|z^2-1\right|=|z|^2+1$, then $z$ lies on
If $\left|z^2-1\right|=|z|^2+1$, then $z$ lies on
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the real axis
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an ellipse
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a circle
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the imaginary axis.
Solution
$\left|z^2-1\right|^2=\left(|z|^2+1\right) \Rightarrow\left(z^2-1\right)\left(\bar{z}^2-1\right)=|z|^4+2|z|^2+1$
$\Rightarrow z^2+\bar{z}^2+2 z \bar{z}=0 \Rightarrow z+\bar{z}=0$
$\Rightarrow R(z)=0 \Rightarrow z$ lies on the imaginary axis.
Asked in: JEE Main 2004
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