Bài 5:
\(\dfrac{\widehat{A}}{2}=\dfrac{\widehat{B}}{3}=\dfrac{\widehat{C}}{4}=\dfrac{\widehat{A}+\widehat{B}+\widehat{C}}{2+3+4}=\dfrac{180^0}{9}=20^0\\ \Rightarrow\left\{{}\begin{matrix}\widehat{A}=40^0\\\widehat{B}=60^0\\\widehat{C}=80^0\end{matrix}\right.\)
Bài 6:
Gọi 3 cạnh là a,b,c(cm;0>a>b>c)
Ta có \(a:b:c=4:7:9\Rightarrow\dfrac{a}{4}=\dfrac{b}{7}=\dfrac{c}{9}\)
Mà \(a=20\)
\(\Rightarrow\left\{{}\begin{matrix}\dfrac{b}{7}=\dfrac{20}{4}=5\\\dfrac{c}{9}=\dfrac{20}{4}=5\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}b=35\\c=45\end{matrix}\right.\)
Vậy cạnh lớn nhất là 45cm
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