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fie ABC un triunghi oarecare unde AB = 12 cm, AC = 15 cm, unghiul A = 60° ,afla BC.​

Răspuns :

BC²=AB²+AC²-2AB×AC×cosA

BC²=12²+15²-2×12×15×cos 60°

BC²=144+225-360×1/2

BC²=144+225-180

BC²=369-180

BC²=189

BC=√189

BC=√(3²×21)

BC=3√21