найти косинус угла А,В,С  если А(3:9) В(0;6) С(4;2)

AB = √ (0-3)^2+(6-9)^2 = √ 9+9 = √ 18BC = √ (4-0)^2+(2-6)^2 = √ 16+16 = √ 32AC = √ (4-3)^2+(2-9)^2 = √ 1+49 = √ 50cos А = АВ^2+AC^2-BC^2/2ABxAC = 18+50-32/2√ 576 = 36/48 = 0,75cos B = AB^2+BC^2-AC^2/2xABxAC = 18+32-50/2√ 900 = 0/60=0cos C = BC^2+AC^2-AB^2/2xBCxAC= 32+50-18/2√ 1600 = 64/80 = 0,8