Question

[Cute Vô Đối]

1,Tính

a, A = \(\dfrac{1}{1.2}\) + \(\dfrac{1}{2.3}\) + \(\dfrac{1}{3.4}\) + . . . + \(\dfrac{1}{2017.2018}\)

b,B = \(\dfrac{5}{2.4}\) + \(\dfrac{5}{4.6}\) + \(\dfrac{5}{6.8}\) + . . . + \(\dfrac{5}{2016.2018}\)

c. C = \(\dfrac{1}{18}\) + \(\dfrac{1}{54}\) + \(\dfrac{1}{108}\) + . . . + \(\dfrac{1}{990}\)

Answer 1

[Lê Trần Khánh Linh]

a, A = 1 - 1/2 + 1/2 - 1/3 + 1/3 -1/4 +... + 1/2017 - 1/2018

A = 1 - 1/2018 = 2017/2018

b, B = 5/2 . ( 1/2 - 1/4 + 1/4 - 1/6 + 1/6 - 1/8 + ... + 1/2016 -1/2018)

B= 5/2 . ( 1/2 - 1/ 2018 )

B = 504/1009

c, C = 1/3.6 + 1/ 6.9 + 1/ 9.12 + ... + 1/ 30.33

C= 1/3 - 1/6 + 1/6 - 1/ 9 + 1/9 - 1/12 + ... + 1/30 - 1/33

C = 1/3 - 1/33

C= 10/33

Answer 2

[Lê Trần Khánh Linh]

phan B mk quên nhân với 5/2

lấy 5/2 . 504/1009 = 1260/1009