Cho $ a, b, c > 0 $ và $m = \min (\left| {a - b} \right|,\left| {a - c} \right|,\left| {c - b} \right|) $ . Chứng minh rằng:
a (dễ chứng minh):
\[\frac{a}{b} + \frac{b}{c} + \frac{c}{a} + 6 \ge \frac{{27(ab + bc + ca + {m^2})}}{{{{(a + b + c)}^2}}}\]
b (khó):
\[\frac{a}{b} + \frac{b}{c} + \frac{c}{a} + 6 \ge \frac{{27(ab + bc + ca + {m^2})}}{{{{(a + b + c)}^2}}}+ {\frac {{m}^{2}}{ \left( a+b+c \right) ^{2}} \left( {\frac {a}{b}}+{
\frac {b}{c}}+{\frac {c}{a}}+{\frac {b}{a}}+{\frac {c}{b}}+{\frac {a}{
c}}-6 \right) }
\]