1.

The complex number z having least positive argument which satisfy the condition `|z - 25i|

Answer» With the given condition `|z-25i| le 15`, we can draw a circle with center `(0,25)` and radius `15`.
Please refer to video for the figure.
From the figure, we can see that,
`P` point will have least positive argument.
Here, `CP = 15, OC = 25 and /_CPO = 90^@`
Then, `OP^2 =OC^2- CP^2 = 25^2-15^2 = 400`
`=>OP = 20`
Let `/_POC = theta`
Then, `sintheta = 15/25 = 3/5, cos theta = 20/25 = 4/5`
So, coordinates of point `P` will be `(OP sintheta,OPcostheta)`.
Coordinates of `P` are `(20(3/5),20(4/5))` that is `(12,16)`.
If we convert it into a complex number, then it will be `12+16i`, which is the required number.


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