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QJEEAdv10Ma05c5: JEE Advanced 2010 Mathematics - Class 11 JEEAdv10Ma05c5 Solution: Let and be two distinct complex numbers let for some real…

Let z1z_1 and z2z_2 be two distinct complex numbers let z=(1−t)z1+tz2z=(1-t) z_1+t z_2 for some real number t with 0 < t < 1 .

If Arg⁡(w)\operatorname{Arg}(w) denotes the principal argument of a nonzero complex number ww , then :

Multiple Choice Options

  • A ∣z−z1∣+∣z−z2∣=∣z1−z2∣\left|z-z_1\right|+\left|z-z_2\right|=\left|z_1-z_2\right|
  • B Arg⁡(z−z1)=Arg⁡(z−z2)\operatorname{Arg}\left(z-z_1\right)=\operatorname{Arg}\left(z-z_2\right)
  • C ∣z−z1zˉ−zˉ1z2−z1zˉ2−zˉ1∣=0\left|\begin{array}{cc}z-z_1 & \bar{z}-\bar{z}_1 \\ z_2-z_1 & \bar{z}_2-\bar{z}_1\end{array}\right|=0
  • D Arg⁡(z−z1)=Arg⁡(z2−z1)\operatorname{Arg}\left(z-z_1\right)=\operatorname{Arg}\left(z_2-z_1\right)

Step-by-Step Verified Solution

amp; Given, z=(1−t)z1+tz2amp;⇒z−z1z2−z1=tamp;⇒arg⁡(z−z1z2−z1)=0.......(i)\begin{aligned} & \text { Given, } z=(1-t) z_1+t z_2 \\\\ & \Rightarrow \frac{z-z_1}{z_2-z_1}=t \\\\ & \Rightarrow \arg \left(\frac{z-z_1}{z_2-z_1}\right) = 0 .......(i) \end{aligned}

⇒arg⁡(z−z1)amp;=arg⁡(z2−z1)z−z1z2−z1amp;=zˉ−zˉ1zˉ2−zˉ1∣z−z1amp;zˉ−zˉ1z2−z1amp;zˉ2−zˉ1∣amp;=0\begin{aligned} \Rightarrow \arg \left(z-z_1\right) & =\arg \left(z_2-z_1\right) \\\\ \frac{z-z_1}{z_2-z_1} & =\frac{\bar{z}-\bar{z}_1}{\bar{z}_2-\bar{z}_1} \\\\ \left|\begin{array}{cc}z-z_1 & \bar{z}-\bar{z}_1 \\ z_2-z_1 & \bar{z}_2-\bar{z}_1\end{array}\right| & =0\end{aligned}

IIT-JEE 2010 Paper 1 Offline Mathematics - Complex Numbers Question 1 English Explanation

AP+PB=AB⇒∣z−z1∣+∣z−z2∣=∣z1−z2∣\begin{gathered}\mathrm{AP}+\mathrm{PB}=\mathrm{AB} \\\\ \Rightarrow\left|z-z_1\right|+\left|z-z_2\right|=\left|z_1-z_2\right|\end{gathered}

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