Bài 5:

`a)` `(x-3)/13 + (x-3)/14 = (x-3)/15 + (x-3)/16`

`=> (x-3)/13 + (x-3)/14 - (x-3)/15 - (x-3)/16 = 0`

`=> (x-3)(1/13 + 1/14 - 1/15 - 1/16) = 0`

Vì `1/13 + 1/14 - 1/15 - 1/16 != 0`

`=> x - 3 = 0`

`=> x = 3`

Vậy `x = 3`

`b)` `(x+1)/65 + (x+3)/63 = (x+5)/61 + (x+7)/59`

`=> ((x+1)/65 + 1) + ((x+3)/63 + 1) = ((x+5)/61 + 1) + ((x+7)/59 + 1)`

`=> (x+66)/65 + (x+66)/63 = (x+66)/61 + (x+66)/59`

`=> (x+66)/65 + (x+66)/63 - (x+66)/61 - (x+66)/59 = 0`

`=> (x+66)(1/65 + 1/63 - 1/61 - 1/59) = 0`

Vì `1/65 + 1/63 - 1/61 - 1/59 != 0`

`=> x + 66 = 0`
`=> x = -66`

Vậy `x = -66`

Bài 6:

`a)` `(29-x)/21 + (27-x)/23 + (25-x)/25 + (23-x)/27 + (21-x)/29 = -5`

`=> ((29-x)/21 + 1) + ((27-x)/23 + 1) + ((25-x)/25 + 1) + ((23-x)/27 + 1) + ((21-x)/29 + 1) = 0`

`=> (50-x)/21 + (50-x)/23 + (50-x)/25 + (50-x)/27 + (50-x)/29 = 0`

`=> (50-x)(1/21 + 1/23 + 1/25 + 1/27 + 1/29) = 0`

Vì `1/21 + 1/23 + 1/25 + 1/27 + 1/29 != 0`

`=> 50 - x = 0`

`=> x = 50`

Vậy `x = 50`

`b)` `(x-10)/30 + (x-14)/43 + (x-5)/95 + (x-148)/8 = 0`

`=> ((x-10)/30 - 3) + ((x-14)/43 - 2) + ((x-5)/95 - 1) + ((x-148)/8 + 6) = 0`

`=> (x-100)/30 + (x-100)/43 + (x-100)/95 + (x-100)/8 = 0`

`=> (x-100)(1/30 + 1/43 + 1/95 + 1/8) = 0`

Vì `1/30 + 1/43 + 1/95 + 1/8 != 0`

`=> x - 100 = 0`

`=> x = 100`

Vậy `x =100`