JEE Advanced | 2018Complex NumbersHard

Question

For a non-zero complex number z, let arg(z) denotes the principal argument with-π< arg(z)  π. Then, which of the following statement(s) is (are) FALSE ?

Options

A.

arg(–1 – i) = 4 =π4 , where i = -1

B.

The function ƒ :  (–π,π], defined by ƒ(t) = arg(–1 + it) for all t R, is continuous at all points of R where i =-1

C.

For any two non-zero complex numbers z1 and z2 Z1Z2 -argZ1+ arg z(Z2)arg  is an integer  multiple of 2π

D.

For any three given distinct complex numbers z1, z2 and z3, the locus of the point z satisfying the  condition arg Z-Z1Z2-Z3Z-Z3Z2-Z1=πlies on a straight line

Solution

(A) arg(–1 – i) = –3π4 ,
(B) ƒ(t) = arg(–1 + it)=π-tan-1,  t0-π-tan-1,  t<0
Discontinuous at t = 0.
(C) argz1z2 -arg (z1)+ arg( z2)
= argz1 – arg(z2) + 2nπ – arg(z1) + arg(z2) = 2nπ.
(D)arg(z-z1)(z2-z3)(z-z3)(z2-z1)=π
(z-z1)(z2-z3)(z-z3)(z2-z1)is real
z, z1, z2, z3 are concyclic.

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