1949*1949-1950*1950+1951*1951-1952*1952+.1999*1999 ji suan

1949*1949-1950*1950+1951*1951-1952*1952+.1999*1999 ji suan

1949 * 1949-1950 * 1950 + 1951 * 1951-1952 * 1952 +. 1999 * 1999 = (1949 + 1950) * (1949-1950) + (1951 + 1952) * (1951-1952) +. + (1999 + 2000) * (1949-2000) - 2000 * 2000 = 4000000 - (1949 + 1950 + 1951 +. + 2000) = 4000000-102674 = 3897326