Let rightangled $\triangle ABC$ be given with right angle at vertex $C$. Let $D$ be foot of altitude from $C$ and let $k$ be circle that touches $BD$ at $E$, $CD$ at $F$ and circumcircle of $\triangle ABC$ at $G$. $a.)$ Prove that points $A$, $F$ and $G$ are collinear. $b.)$ Express radius of circle $k$ in terms of sides of $\triangle ABC$.

Find minimal number of divisors that can number $|2016^m-36^n|$ have,where $m$ and $n$ are natural numbers.

In two neigbouring cells(dimensions $1\times 1$) of square table $10\times 10$ there is hidden treasure. John needs to guess these cells. In one $\textit{move}$ he can choose some cell of the table and can get information whether there is treasure in it or not. Determine minimal number of $\textit{move}$'s, with properly strategy, that always allows John to find cells in which is treasure hidden.

Let $a,b,c\in \mathbb{R}^+$, prove that: $$\frac{2a}{\sqrt{3a+b}}+\frac{2b}{\sqrt{3b+c}}+\frac{2c}{\sqrt{3c+a}}\leq \sqrt{3(a+b+c)}$$