Let $Z$ and $W$ be complex numbers such that $|Z|=|W|$, and $\arg Z$ denotes the principal argument of $Z$.…

Let $Z$ and $W$ be complex numbers such that $|Z|=|W|$, and $\arg Z$ denotes the principal argument of $Z$. Statement 1:If $\arg Z+\arg W=\pi$, then $Z=-\bar{W}$. Statement 2: $|Z|=|W|$, implies arg $Z-\arg \bar{W}=\pi$.
  1. Statement 1 is true, Statement 2 is false.
  2. Statement 1 is true, Statement 2 is true, Statement 2 is a correct explanation for Statement 1.
  3. Statement 1 is true, Statement 2 is true, Statement 2 is not a correct explanation for Statement 1.
  4. Statement 1 is false, Statement 2 is true.

Solution

Let $|Z|=|\mathrm{W}|=r$ $ \Rightarrow Z=r e^{i \theta}, \mathrm{W}=r e^{i \phi} $ where $\theta+\phi=\pi$ $ \therefore \quad \bar{W}=r e^{-i \phi} $ Now, $Z=r e^{i(\pi-\phi)}=r e^{i \pi} \times e^{-i \phi}=-r e^{-i \phi}$ $ =-\bar{W} $ Thus, statement-1 is true but statement- 2 is false

Asked in: JEE Main 2012 (19 May Online)

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