H a i c ô b ạ n c ó n g à y s i n h l à $\it{27}\,/\,11$ $\it{\&}$ $\it{21}\,.\,\it{8}$ $($$.$$)$ C h ứ n g m i n h r ằ n g
$$\pi^2- 2\,\pi\,w\geqq {\it{27}}\,/\,{\it{11}}\,(\,2\,\pi\,\sin\,w- 4\,w\,)+ {\it{21}}\,.\,{\it{8}}$$
Đ ề t ặ n g
B í m ậ t
D ấ u b ằ n g x ả y r a $<$$=$$>$ $w= \frac{5}{2}\,\pi+ \arcsin\left ( \left \{ \frac{{\it{27}}}{{\it{11}}} \right \}^{\,-\,1}- \frac{2}{\pi} \right )$
