va rog exercitiul 11

1/1 - 1/2 = (2-1)/2 = 1/2 = 1/·2
1/2 - 1/3 = (3-2)/6 = 1/6 = 1/2·3
1/3 - 1/4 = (4-3)/12 = 1/12 = 1/3·4
1/1·2 + 1/2·3 + ... + 1/99·100 =
= 1/1 - 1/2 + 1/2 - 1/3 + ... + 1/99 - 1/100
= 1/1 - 1/100
= (100-1)/100
= 99/100