Samyak Jain
Last Activity: 7 Years ago
|z – 2 – i| = 4 or |z – (2 + i)| = 4
Above equation represents a circle centred at (2,1) with radius 4 units.

Eq
n of circle is (x – 2)
2 + (y – 2)
2 = 16 ................(1)
Minimum value of |3z-6+15i| means minimum value of
3|z – (2 – 5i)|.
First we’ll find the minimum value of |z – (2 – 5i)| & multiply it by 3.
It denotes least distance from a point on the circle & point (2, – 5).
(2, – 5) lies below the circle in coordinate axes system.
Line through center (2,1) & (2, – 5) is parallel to y-axis &
its eqn is x = 2 …................(2)
points of intersection of (1) & (2) are (2,5) & (2, – 3).
By geometry, (2, –3) is nearest to (2, –5) of all points on the circle.

Distance between (2, –3) & (2, –5) is 2 units, i.e.,
minimum value of |z – (2 – 5i)| is 2 and hence
the minimum value of |3z-6+15i| = 3|z – (2 – 5i)| = 3*2
= 6