Question

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

Answer 1

[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]