Giúp nốt 2 bài này thôi ak

Bài `7:`

`B = (0,5- 3/17 + 3/37)/(5/6 - 5/17 + 5/37) + (0,5 - 1/3 + 1/4 -0,2)/(7/5 - 7/4 + 7/3 - 3,5)`

` = (3/6 - 3/17 + 3/37)/(5/6 - 5/17 + 5/37) + (1/2 - 1/3 + 1/4 - 1/5)/(7/5 - 7/4 + 7/3 - 7/2)`

` = (3 . (1/6 - 1/17 + 1/37))/(5 . (1/6 - 1/17 + 1/37)) + (1/2 - 1/3 + 1/4 - 1/5)/(-7 . (1/2 - 1/3 + 1/4 - 1/5)`

`  = 3/5 + 1/(-7)`

` = 3/5 - 1/7`

` = 16/35`

Vậy `B = 16/35`

``

Bài `8:`

`((1 + 2+ 3 + ...+100)(1/2 - 1/3 -1/7-1/9) (63. 1,2 - 21 . 3,6))/(1-2+3-4+..+99-100)`

` = ((1 + 2+ 3 + ...+100)(1/2 - 1/3 -1/7-1/9) (63. 6/5 - 21 . 18/5))/(1-2+3-4+..+99-100)`

` = ((1 + 2+ 3 + ...+100)(1/2 - 1/3 -1/7-1/9) (378/5 - 378/5))/(1-2+3-4+..+99-100)`

` = ((1 + 2+ 3 + ...+100)(1/2 - 1/3 -1/7-1/9) 0/(1-2+3-4+..+99-100)`

` = 0/(1-2+3-4+..+99-100)`

` = 0`