1) 7☆5=7+8+9+10+11=45
☆表示從7開(kāi)始,連續(xù)加5個(gè)數(shù).
2) （1+1/2）×（1-1/2）×（1+1/3）×（1-1/3）×……×（1+1/99）×（1-1/99）
=(3/2) × (1/2) × (4/3) × (2/3) × (5/4) × (3/4) ×.×(99/98) × (97/98) × (100/99) × (98/99)
=[(3/2) × (4/3)× (5/4) ×.×(99/98) × (100/99)]× [(1/2) × (2/3) × (3/4) ×.×(97/98) × (98/99)]
=[(1/2) × (1/1)× (1/1) ×.×(1/1) × (100/1)]× [(1/1) × (1/1) × (1/1) ×.×(1/1) × (1/99)]
=[100/2] × [1/99]
=50/99
把所有（1+1/n）的放一起,把所有（1-1/n）的放一起第一題有什么規(guī)律么？