Cho \(\Delta ABC\) c...

B

- Hướng dẫn giải

Xét ΔABC có: \( \widehat A + \widehat B + \widehat C = {180^0}\)

Ta có: \(\left\{ \begin{array}{l} \widehat B + \widehat C = {100^0}\\ \widehat B - \widehat C = {20^0} \end{array} \right. \to \left\{ \begin{array}{l} \widehat B = {60^0}\\ \widehat C = {40^0} \end{array} \right.\)

\( \widehat C < \widehat B < \widehat A=>AB<AC<BC\)