For any complex number w = c + i d , let arg w ∈ ( - π , π ] , where i = - 1 . Let α…

For any complex number w=c+id, let argw(-π,π], where i=-1. Let α and β be real numbers such that for all complex numbers z=x+iy satisfying argz+αz+β=π4, the ordered pair (x, y) lies on the circle x2+y2+5x-3y+4=0
Then which of the following statements is(are) TRUE?
  1. α=-1
  2. αβ=4
  3. αβ=-4
  4. β=4

Solution

argz+αz+β=π4 represents an arc of a circle and -α,0 & -β,0 subtends an angle π4 on z

Given, x2+y2+5x-3y+4=0

Centre -52,32, r=254+94-4=32

Angle made by (-α,0) & (-β,0) at the centre C is π2

Using rotation of complex numbers, we get

-α--52+32i-β--52+32i=1·eiπ2=i

-α+52-32i=-iβ+52i+32

α-iβ=1-4i

α, βR

α=1, β=4

Asked in: JEE Advanced 2021 (Paper 1)

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