Let A = θ ∈ - π 2 , π : 3 + 2 i   s i n θ 1 - 2 i   s i n θ  …

Let A=θ-π2,π:3+2isinθ1-2i sinθ is purely imaginary . Then the sum of the elements in A is:
  1. 5π6
  2. π
  3. 2π3
  4. 3π4

Solution

Given complex number is z=3+2isinθ1-2isinθ

z=(3+2isinθ)(1+2isinθ)(1+4sin2θ)

Since given complex number is purely imaginary

Re(z)=0

3-4sin2θ=0

sinθ=±32

θ=-π3,π3,2π3

sum of all possible values of θ=2π3 .

Asked in: JEE Main 2019 (09 Jan Shift 1)

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