a) Áp dụng ĐL Pytago ta có:
\(AC^2=AB^2+BC^2=3^2+4^2=25\Rightarrow AC=5\left(cm\right)\)
Ta có: \(sin\widehat{A}=\dfrac{BC}{AC}=\dfrac{4}{5}\); \(cos\widehat{A}=\dfrac{AB}{AC}=\dfrac{3}{5}\)
\(\Rightarrow tan\widehat{A}=\dfrac{4}{3};cot\widehat{A}=\dfrac{3}{4}\)
b) Ta có \(sin\widehat{A}=\dfrac{4}{5}\Rightarrow\widehat{A}\approx53^0\)
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