90個埃及數:1/2,1/3,1/4,1/5,…,1/90,1/91,挑10個,加正負號,使它們的和為-1

90個埃及數:1/2,1/3,1/4,1/5,…,1/90,1/91,挑10個,加正負號,使它們的和為-1

-1=-1/5-1/6-1/8-1/9-1/10-1/12-1/15-1/18-1/20-1/24