Theo định lí Pi-Ta-Go( T dz hơn you ) thì:
\(\widehat{A}+\widehat{B}+\widehat{C}=180^o\)
Biết:
\(\left\{{}\begin{matrix}\widehat{A}=2\widehat{B}\\\widehat{B}=3\widehat{C}\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}\dfrac{\widehat{A}}{2}=\dfrac{\widehat{B}}{1}\\\dfrac{\widehat{B}}{3}=\dfrac{\widehat{C}}{1}\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}\dfrac{\widehat{A}}{6}=\dfrac{\widehat{B}}{3}\\\dfrac{\widehat{B}}{3}=\dfrac{\widehat{C}}{1}\end{matrix}\right.\)
\(\Rightarrow\dfrac{\widehat{A}}{6}=\dfrac{\widehat{B}}{3}=\dfrac{\widehat{C}}{1}\)
Áp dụng tính chất dãy tỉ số bằng nhau ta có:
\(\dfrac{\widehat{A}}{6}=\dfrac{\widehat{B}}{3}=\dfrac{\widehat{C}}{1}=\dfrac{\widehat{A}+\widehat{B}+\widehat{C}}{6+3+1}=\dfrac{180^o}{10}=18^o\)
\(\Rightarrow\left\{{}\begin{matrix}\widehat{A}=18^o.6=108^o\\\widehat{B}=18^o.3=54^o\\\widehat{C}=18^o.1=18^o\end{matrix}\right.\)
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