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Laurentiu09
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in ∆ABC AB=3 BC=2 AC=4 . Calculati cos A

Răspuns :

[tex]\text{Aplicam teorema cosinusului:}\\ BC^2=AB^2+AC^2-2\cdot AB\cdot AC\cdot \cos A\\ \cos A=\dfrac{AB^2+AC^2-BC^2}{2\cdot AB\cdot AC}\\ \cos A=\dfrac{9+16-4}{2\cdot 3\cdot 4}\\ \cos A=\dfrac{21}{24}=\boxed{\dfrac{7}{8}}[/tex]

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