[Math] Greatest value of $|z|$ such that $|z-2i|\le2$ and $ 0\le \arg(z+2)\le 45^\circ$

complex numbersgeometric-inequalities

I've to sketch the complex numbers $z$ satisfying both the inequalities

$$|(z-2i)|\le2,$$
$$ 0\le \arg(z+2)\le 45^\circ.$$

I was able to sketch and shade the region that satisfies both inequalities; here is my Argand diagram:

However, I've a problem in getting the greatest value of $|z|$, i.e. the maximum length of $z$ from $(0,0).$ It should come to around 3.70.

Best Answer

if you parametrize the circle of constraint it is $(2\cos t,2\sin t +2)$ with $t=0$ corresponding to the point $(2,2)$. so:

$$ \frac18 |z|^2 = \frac12 (\cos^2 t +\sin^2 t + 2 \sin t +1 )= 1+ \sin t $$