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4-1.Complex numbers
hard
Let $z$ be a complex number such that $\left| z \right| + z = 3 + i$ (where $i = \sqrt { - 1} $). Then $\left| z \right|$ is equal to
A
$\frac{{\sqrt {34} }}{3}$
B
$\frac{5}{3}$
C
$\frac{{\sqrt {41} }}{4}$
D
$\frac{5}{4}$
(JEE MAIN-2019)
Solution
$z\, = \,x\, + \,iy$
$\sqrt {{x^2} + {y^2}} \, + \,x\, + \,iy\, = \,3\, + \,i$
$ \Rightarrow \,y = 1$
$\sqrt {{x^2} + 1} \, + \,x = 3 \Rightarrow {x^2}\, + \,1 = 9 – 6x + {x^2}$
$ \Rightarrow \,x = \frac{4}{3}$
$|z|\, = \,\sqrt {{x^2}\, + \,{y^2}} \, = \,\frac{5}{3}$
Standard 11
Mathematics