Question

Tính

a) A= 1/2.9 + 1/9.7 + 1/7.19 +....+ 1/252.509

b) B= 1/10.9 + 1/18.13 + 1/26.17+.... + 1/802.405

Nhanh nhaaa iuuu

Answer 1

a)Ta có: 

A= 1/2.9 + 1/9.7 +...+1/252.509

  = 2/5.(5/4.9 + 5/9.14 + 5/14.19 +...+ 1/504.509)

  = 2/5.(1/4 - 1/9 + 1/9 - 1/14 + 1/14 - 1/19 +...+ 1/504 - 1/509)

  = 2/5.(1/4 - 1/509)

  = 101/1018

Vậy A = 101/1018

b)Ta có:

B= 1/10.9 +1/18.13 + 1/26.17 +...+ 1/802.405)

  = 1/4.(8/10.18 + 8/18.26 + 8/26.34 +...+ 8/802.810)

  = 1/4.(1/10 - 1/18 + 1/18 - 1/26 + 1/26 - 1/34 +...+ 1/802 - 1/810)

  = 1/4.(1/10 - 1/810)

  = 2/81

Vậy B= 2/81

Tk mình nha!!!

Answer 2

a,A=101/1018 b,B=2/81

Answer 3

\(\frac{n}{n}\)

Answer 4

Tôi không biết làm sai rồi phải là nhân với5/2 chứ