fie Δ ABC AB =c AC = b mas< A = α
construim inaltimea BD (BD_|_ AC)
in ΔABD BD = ABsinα AD = c·cosα
in ΔBDC DC =b - c·sinα AD = c·cosα BC² = a² = c²cos²α + (b - c·sinα)² =
= c²cos²α + b² - 2bcsinα +c²sin²α = c² + b² - 2bcsinα a = √(c² +b² -2bcsinα)
P = a + b + c
