(a + b + c)² = (a + b + c) × (a + b + c) = a² + ab + ac + ab + b² + bc + ac + bc + c² = a² + b² + c² + 2ab + 2bc + 2ac
i) (10 + 10 + 10)² = 30² = 900
10² + 10² + 10² + 2 × 10 × 10 + 2 × 10 × 10 + 2 × 10 × 10 =
= 100 + 100 + 100 + 200 + 200 + 200 = 900
ii) (2 + 3 + 4)² = 9² = 81
2² + 3² + 4² + 2 × 2 × 3 + 2 × 2 × 4 + 2 × 3 × 4 = 4 + 9 + 16 + 12 + 16 + 24 =
29 + 28 + 24 = 81