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Q. If an equilateral triangle $A B C$ with vertices at $z_1, z_2$ and $z_3$ be inscribed in a circle $|z|=2$ and again a circle is inscribed in $\triangle ABC$ touching sides $AB , BC$ and $CA$ at $D \left( z _4\right), E \left( z _5\right)$ and $F \left( z _6\right)$ respectively.
Column I Column II
P Value of $\operatorname{Re}\left( z _1 \overline{ z }_2+ z _2 \overline{ z }_3+ z _3 \overline{ z }_1\right)$ is equal to 1 2
Q If $\frac{4 z_1}{z_3}=a(-1+i \sqrt{3})$ then a is equal to 2 -6
R $\quad\left|z_1+z_2\right|^2+\left|z_2+z_3\right|^2+\left|z_3+z_1\right|^2$ is equal to 3 12
S If $P$ is any point on incircle, then $DP ^2+ EP ^2+ FP ^2$ is 4 6

Complex Numbers and Quadratic Equations

Solution:

(A)image
$\Theta \left|z_1-z_2\right|^2=\left|z_1\right|^2+\left|z_2\right|^2-2 \operatorname{Re}\left(z_1 \bar{z}_2\right) $
$\Rightarrow (2 \sqrt{3})^2=2^2+2^2-2 \operatorname{Re}\left(z_1 \bar{z}_2\right)$
$\Rightarrow \operatorname{Re}\left(z_1 \bar{z}_2\right)=-2$
Similarly, $\operatorname{Re}\left( z _2 \overline{ z }_3\right)=-2$
& $ \operatorname{Re}\left( z _3 \overline{ z }_1\right)=-2$
$\therefore \operatorname{Re}\left( z _1 \overline{ z }_2+ z _2 \overline{ z }_3+ z _3 \overline{ z }_1\right)=-6$
(B) $ \Theta \frac{ z _1-0}{ z _3-0}= e ^{\frac{ i 2 \pi}{3}} \Rightarrow \frac{ z _1}{ z _3}=\left(-\frac{1}{2}+\frac{ i \sqrt{3}}{2}\right) \Rightarrow \frac{4 z _1}{ z _3}=2(-1+ i \sqrt{3}) $
$\therefore a =2$
(C)$\left|z_1+z_2\right|^2+\left|z_2+z_3\right|^2+\left|z_3+z_1\right|^2 =2\left(\left|z_1\right|^2+\left|z_2\right|^2+\left|z_3\right|^2\right)+2\left(\operatorname{Re}\left(z_1 \bar{z}_2+z_2 \bar{z}_3+z_3 \bar{z}_1\right)\right)$
$ =2(4+4+4)+2(-6)=12$
(D) $ DP ^2+ EP ^2+ FP ^2=\left| z - z _4\right|^2+\left| z - z _5\right|^2+\left| z - z _6\right|^2=3| z |^2+\left| z _4\right|^2+\left| z _5\right|^2+\left| z _6\right|^2=6 $