Q: Let ‘z’ be a complex number and ‘a’ be a real parameter such that z^{2} + az + a^{2} = 0, then

(A) locus of z is a pair of straight lines

(B) locus of z is a circle

(C) arg(z) = ± 2π/3

(D) |z| =|a|

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Ans: (A),(C) ,(D)

Sol: z

^{2}+ az + a^{2}= 0⇒ z = aw, aw^{2} ( where ‘w’ is non real root of cube unity )

⇒ locus of z is a pair of straight lines

and arg (z) =arg(a) + arg(w) or arg(a) + arg(w^{2})

⇒ arg(z) = ± 2π/3

also, |z| = |a||w| or |a| |w^{2}| ⇒ |z| = |a|

Hence (A), (C) and (D) are the correct answers.