Tính T = (1002 + 982 + … + 22) – (992 + 972 +…+12).
Giải thích
T = (1002 + 982 + … + 22) – (992 + 972 +…+12)
T = (1002 – 992) + (982 – 972) +…+ (22 – 12)
T = (100 – 99) (100 + 99) + (98 – 97) (98+97) + … + (2 – 1) (2 + 1)
T = 1. (100 + 99) + 1. (98 + 97) + … + 1. (2 + 1)
T = 100 + 99 + 98 + … + 2 + 1
T=100.100+12=5050