C.N.'

found a simplier method.. :)

z₂ - z₃z₁ - z₃ = e^i∂
here ∂=60° (as triangle is equilateral).

thus,e^i∂ = cos∂ +isin∂ = 1+√3i
2.

thus,
-1 + bi-a + i = 1+√3i2.

thus,on simplifying.
-2+2bi = -√3ai - √3 - a +i.

equating the real and imaginary co-efficients weget,
a=b= 2 - √3

thus...
i get (A) and (C) as answer..

Yes you are getting the right answers.
Thank you very much.