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Question: If I<sub>m</sub>\(\left( \frac{z - 1}{2z + 1} \right)\)= –4, then locus of z is-...

If Im(z12z+1)\left( \frac{z - 1}{2z + 1} \right)= –4, then locus of z is-

A

Ellipse

B

Parabola

C

Straight line

D

Circle

Answer

Circle

Explanation

Solution

Sol. Put z = x + iy

Ž Im (x1+iy2x+1+2iy)\left( \frac{x - 1 + iy}{2x + 1 + 2iy} \right)=–4

=2y(x1)+y(2x+1)(2x+1)2+4y2\frac{- 2y(x - 1) + y(2x + 1)}{(2x + 1)^{2} + 4y^{2}}= –4

We get 16x2 + 16y2 + 16x + 3y + 4 = 0 (Eq. of Circle)