Resposta:
[tex]\cos{\alpha} = \dfrac{2}{18}[/tex]
Explicação passo a passo:
[tex]\overline{AB} = 3\\\overline{AC} = 3\\\overline{BC} = 4\\\overline{BC} = \sqrt{\overline{AB}^2 + \overline{AC}^2 - (2 \times \overline{AB}\times \overline{AC}) \cos{\alpha}}\\4 = \sqrt{3^2 + 3^2 - (2\times 3 \times 3) \cos{\alpha}}\\4 = \sqrt{18 - 18\cos{\alpha}}\\16 = 18 - 18\cos{\alpha}\\18\cos{\alpha} = 2\\\cos{\alpha} = \dfrac{2}{18}\\\alpha = \arccos{\dfrac{2}{18}}\\\alpha = 83,62^{\circ}[/tex]
