Cho $\it{3}$ số thực dương $\it{a},\,\it{b},\,\it{c}$$,$ chứng minh rằng$:$
$$\frac{\it{a}}{\it{b}+ \it{c}}+ \frac{\it{b}}{\it{c}+ \it{a}}+ \frac{\it{c}}{\it{a}+ \it{b}}\geqq \frac{\it{39}}{\it{4}}\left [ \frac{\it{2}\,\it{c}^{\,\it{2}}}{\it{(}\,\,\it{a}+ \it{b}\,\,\it{)}^{\,\it{2}}}- \frac{\it{c}}{\it{a}+ \it{b}} \right ]$$