\(đặt:AB=c;BC=a;AC=b\)
\(2cosB-sinC=\dfrac{1}{2}\Leftrightarrow\dfrac{2c}{a}-\dfrac{c}{a}=\dfrac{1}{2}\Leftrightarrow\dfrac{c}{a}=\dfrac{1}{2}\Leftrightarrow2c=a\left(1\right)\)
\(gọi\) \(I\) \(trung\) \(điểmBC\Rightarrow AI=BM=\dfrac{BC}{2}=\dfrac{a}{2}\Leftrightarrow2AI=a\left(2\right)\)
\(\left(1\right)\left(2\right)\Leftrightarrow AI=c=BI\Rightarrow ABI\) đều \(\Rightarrow B=60^o;C=30^o\)
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