A=1/2 +1/14 +1/35 +1/65 + 1/104 +1/152 +1/209+1/275 Tinh A

Đáp án:

`A=1/2 +1/14 +1/35 +1/65 + 1/104 +1/152 +1/209+1/275`

`A = 2/4 + 2/28 + 2/70 + 2/130 + 2/208 + 2/304 + 2/418 + 2/550`

`A = 2/(1.4) + 2/(4.7) + 2/(7.10) + 2/(10.13) + 2/(13.16) + 2/(16.19) + 2/(19. 22) + 2/(22.25)`

`A = 3/3.(2/(1.4) + 2/(4.7) + 2/(7.10) + 2/(10.13) + 2/(13.16) + 2/(16.19) + 2/(19. 22) + 2/(22.25))`

`A = 2/3.(3/(1.4) + 3/(4.7) + 3/(7.10) + 3/(10.13) + 3/(13.16) + 3/(16.19) +3/(19. 22) + 3/(22.25))`

 `A = 2/3.(1 - 1/4 + 1/4 - 1/7 + 1/7 - 1/10 + ..... + 1/22 - 1/25)`

`A = 2/3.(1 - 1/25)`

`A = 2/3 . 24/25`

`A = 16/25`

`#dariana`