Вправи 1001 - 1100 » 1005

Обчисли зручним способом: 1) 1 + 3 + 5 + 7 + ... + 97 + 99 = (99 + 1) + (98 + 2) + (97 + 3) … (51 + 49) + 50 = 100 • 49 + 50 = 4900 + 50 = 4950 2) 2 + 4 + 6 + ... + 98 + 100 – 1 – 3 – 5 – ... – 97 – 99 = (2 – 1) + (4 – 3) + .. (100 – 99) = 1 • 99 = 99