cosA =（300^2+300^2-530^2)/2*300*300 =-1009/1800
角A =π - arccos(1009/1800) ≈124.09°
cosB = (530^2+300^2-300^2)/2*530*300 =53/60
角B =arccos(53/60) ≈27.95°
角C =π + arccos(1009/1800) - arccos(53/60) ≈ 27.95°
cosA =（300^2+300^2-530^2)/2*300*300 =-1009/1800
角A =π - arccos(1009/1800) ≈124.09°
cosB = (530^2+300^2-300^2)/2*530*300 =53/60
角B =arccos(53/60) ≈27.95°
角C =π + arccos(1009/1800) - arccos(53/60) ≈ 27.95°