Let z be a unimodular complex number having the argument θ, 0<θ<π2 and satisfying the relation |z−3i|=3, then arg(cotθ−6z) is
A
π4
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B
π3
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C
π2
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D
3π4
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Solution
The correct option is Cπ2 From polar form of complex numbers, z=|z|(cosθ+isinθ)
As z is uni modular, z=cosθ+isinθ
We have |z−3i|=3 ⇒|cosθ+i(sinθ−3)|=3⇒√cos2θ+(sinθ−3)2=3⇒cos2θ+(sinθ−3)2=9⇒cos2θ+sin2θ−6sinθ+9=9⇒1−6sinθ=0⇒sinθ=16…(1)
Now, cotθ−6z=cotθ−6(cosθ+isinθ)=cotθ−6(cosθ−isinθ)=cotθ−6sinθ(cotθ−i)
By equation (1) =cotθ−cotθ+i=i