AC = 28 cm + 12 cm = 40 cm
teorema bisectoarei : AB / BC = 28 / 12 = 7 / 3
AB = 7BC / 3
AB - BC =18 ; 7BC /3 - BC = 18 numitor 3
7 BC - 3 BC =18·3
4 BC = 54 ; BC = 54 / 4 = 27 / 2 cm
AB = 7 · 27 / 2 ·3 = 7 ·9 / 2 = 63 / 2 cm
perim = AB +BC + AC = 63/ 2 cm + 27 / 2 cm + 40 cm =
= 90 / 2 cm + 40 cm = 45 cm + 40 cm = 85 cm