Воспользуемся теоремой косинусов
b²+c² - a² 5,12²+6,34²-4,48²
cos∠A= -------------------- = ----------------------------- =
2bc 2·5,12·6,34
26,2144+40,1956-20,0704
= --------------------------------------- ≈ 0,7138
64,9216
∠A ≈ 45°30'
a²+c²-b² 4,48²+6,34²-5,12² 20,0704+40,1956-26,2144
cos∠B= ------------- = -------------------------- = ------------------------------------- =
2ac 2·4,48·6,34 56,8064
= 0,5994
∠B ≈ 36°50'
∠C=180° - (45°30'+36°50')=180°- 82°20' = 97°40'