Question

Bạn nào giải được mình cho 10 cái like thật đó

A=\(\frac{10}{56}+\frac{10}{140}+\frac{10}{260}+.....+\frac{10}{1400}\)

Answer 1

A =  10/56 + 10/140 + 10/260 + .......+ 10/1400

A = 5/28 + 5/70 + 5/130 +.........+ 5/700

3A/5 = 3/4.7 + 3/7.10 + 3/10.13 +.......+ 3/25.28

3A/5 = 1/4 - 1/7 + 1/7 - 1/10 + 1/10 - 1/13 +........+ 1/25 - 1/28

3A/5 = 1/4 - 1/28

3A/5 = 3/14

A = 3/14 . 5/3

A = 5/14

Vậy A = 5/14

Answer 2

A= 5/3.(3/28+3/70+3/130+...+3/700)                                                                                                               A=5/3.(3/4.7+3/7.10+3/10.13+...+3/25.28)

A=5/3.(1/4-1/7+1/7-1/10+1/10-1/13+...+1/25-1/28)

A=5/3(1/4-1/28)

A=5/3.(7/28-1/28)

A=5/3.3/14

A=5/14