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Question: If \|z – 2 – i\| = \|z\| sin \(\left( \frac{\pi}{4} - \arg z \right)\) then locus of z is/ are...

If |z – 2 – i| = |z| sin (π4argz)\left( \frac{\pi}{4} - \arg z \right) then locus of z is/ are

A

Ellipse

B

Circle

C

Parabola

D

Pair of straight lines

Answer

Parabola

Explanation

Solution

Sol. |(x – 2) + i (y – 1)| = |z| (12cosθ12sinθ)\left( \frac{1}{\sqrt{2}}\cos\theta - \frac{1}{\sqrt{2}}\sin\theta \right)

q = arg z

Ž (x2)2+(y1)2\sqrt{(x - 2)^{2} + (y - 1)^{2}}

= 12\frac{1}{\sqrt{2}}|z| cos q – 12\frac{1}{\sqrt{2}} |z| sin q

= 12\frac{1}{\sqrt{2}} (x – y)

Ž parabola with vertex (2, 1)

directrix x – y = 0