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4-1.Complex numbers
normal
If complex numbers $(x -2y) + i(3x -y)$ and $(2x -y) + i(x -y + 6)$ are conjugates of each other, then $|x + iy|$ is $(x,y \in R)$
A
$1$
B
$\sqrt2$
C
$2$
D
$4$
Solution
$(x-2 y)+i(3 x-y)=(2 x-y)-i(x-y+6)$
comparing real and imaginary parts
$x+y=0 $ and $2 x-y+3=0$
$\Rightarrow x=-1, y=1$
$|x+i y|=\sqrt{2}$
Standard 11
Mathematics