Ta có:
cosA=b2+c2−a22bc=852+542−52,122.85.54≈0,81
=> cosA=b2+c2−a22bc=852+542−52,122.85.54≈0,81
A^≈36∘
cosB=a2+c2−b22ac=52,12+542−8522.52,1.54≈−0,28
=> B^≈106∘28′
=> C=C^=180∘−A^−B^=180∘−36∘−106∘28′=37∘32′