Question

va rooooog
dau coroana​

Answer 1

Răspuns:

Deducem o formula :

1/a*b = b-a/a*b = b/a*b - a/a*b =

= 1/a - 1/b

Unde b = a+1!!

S = 1/2*3 + 1/3*4 + ... + 1/2018*2019

S = 1/2 - 1/3 + 1/3 - 1/4 + ... +

1/2018 - 1/2019

1/3 se reduce

1/4 se reduce

...............

1/2018 se reduce

Ramane S = 1/2 - 1/2019

S = 2019/4038 - 2/4038

S = 2017/4038