[tex]\begin{gathered} \text{Law of Cosine} \\ BC^2=AB^2+AC^2-2\times AB\times AC\times\cos A \\ 55^2=35^2+50^2-2\times35\times50\times\cos A \\ 3025=1225+2500-3500\times\text{cosA} \\ -3500\times\cos A=3025-1225-2500 \\ -3500\times\cos A=-700 \\ \cos A=\frac{700}{3500} \\ A=\cos ^{-1}(0.2) \\ A=78.46^{\circ} \end{gathered}[/tex]
