Cách làm cho bạn:
Ta có:
a) $\widehat{A}=\widehat{B}=\widehat{C}=180:3=60^{\circ}$;
b)
$\widehat{B}+\widehat{C}=180−\widehat{A}=110^{\circ}$
mà $\widehat{C}−\widehat{B}=20^{\circ}$
=>$\widehat{B}=(110−20):2=45^{\circ}$
$\widehat{C}=110−45=65^{\circ}$
c)
Ta có:
$\frac{A}{1}=\frac{B}{2}=\frac{C}{3}=\frac{A+B+C}{1+2+3}=\frac{180}{6}=30^{\circ}$
=>$A=30^{\circ},\widehat{B}=60^{\circ},\widehat{C}=90^{\circ} $
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