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જો $\left| {z - 3 + 2i} \right| \leq 4$ હોય તો $\left| z \right|$ ની મહતમ અને ન્યૂનતમ કિમત વચ્ચેનો તફાવત કેટલો હશે ?
$\sqrt {13}$
$2\sqrt {13}$
$8$
$4 + \sqrt {13}$
Solution

given equation represents the circle with center (3,-2) and is of radius $( R )=4$
$| z |$ represents the distance of point 'z' from origin
Greatest and least distances occur along the normal through the origin Normal always passes through center of circle
From figure; let PQ be the normal through origin 'O' and $C$ be its center (3,-2)
it is clear that OP is the least distance
and $OQ$ is the greatest distance
From diagram; $OP = CP – OC$ and $OQ = CQ + OC$
Here, $CP = CQ = R =4$
$OC =\sqrt{(3-0)^{2}+(-2-0)^{2}}$
$\Rightarrow OC =\sqrt{13}$
$\therefore OP = CP – OC$
$\Rightarrow OP =4-\sqrt{13}$
$\therefore$ Least distance $OP =4-\sqrt{13}$
and $\quad OQ = CQ + OC$
$\Rightarrow OQ =4+\sqrt{13}$
$\therefore$ Greatest distance $= OQ =4+\sqrt{13}$
Difference between greatest and least distance $=0 Q-O P=(4+\sqrt{13})-(4-\sqrt{13})$
$\Rightarrow$ Difference $=2 \sqrt{13}$
final answer=2 $\sqrt{13}$
the correct option is 'B'