Làm bài 3 và 4 ạ cảm ơn

`3.`

`a,` `(-11)/8 . 19/3 + 19/3 . (-5)/8`

`= 19/3 . ((-11)/8+(-5)/8)`

`= 19/3 . (-2)`

`= (-38)/3`

`b,` `(6 - 2/3 + 1/2) - (5 + 5/3 - 3/2) - (3 - 7/3 + 5/2)`

`= 6 - 2/3 + 1/2 - 5 - 5/3 + 3/2 - 3 + 7/3 - 5/2`

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

`= -2 + 0 + 1/2`

`= -2 + 1/2`

`= (-5)/2`

`c,` `((-3)/7 + 1/12) : (-5)/6 - ((-10)/7 + 13/12) : (-5)/6`

`= [((-3)/7 + 1/12) - ((-10)/7 + 13/12)] : (-5)/6`

`= [((-3)/7 + 1/12 + 10/7 - 13/12)] : (-5)/6`

`= [((-3)/7 + 10/7) - (1/12 - 13/12)] : (-5)/6`

`= (1 - 1) : (-5)/6`

`= 0 : (-5)/6`

`= 0`

`d,` `E = 1/(1.7) + 1/(7.13) + 1/(13.19) + ... + 1/(31.37)`

`E = 1 - 1/7 + 1/7 - 1/13 + 1/13 - 1/19 + ... + 1/31 - 1/37`

`E = 1 - 1/37`

`E = 37/37 - 1/37`

`E = 36/37`

Vậy, `E = 36/37`

`e,` `((-25)/27 - 31/42) - ((-7)/27 - 3/42)`

`= (-25)/27 - 31/42 + 7/27 + 3/42`

`= ((-25)/27+7/27) + ((-31)/42 + 3/42)`

`= (-18)/27 + (-28)/42`

`= (-4)/3`

`f,` `7/8 : (2/9 - 1/18) + 7/8 : (1/36 - 5/12)`

`= 7/8 : 3/18 + 7/8 : (-14)/36`

`= 7/8 . 18/3 + 7/8 . (-36)/14`

`= 7/8 . (18/3 + (-36)/14)`

`= 7/8 . 24/7`

`= 3`

`4.`

`a,` `5/8 + 1/4 . (2x - 1) = 5/4`

`->``1/4 . (2x - 1) = 5/4 - 5/8`

`->``1/4 . (2x - 1) = 5/8`

`->``2x - 1 = 5/8 : 1/4`

`->``2x - 1 = 5/2`

`->``2x = 5/2 + 1`

`->``2x = 7/2`

`->``x = 7/2 : 2`

`->``x = 7/4` 

Vậy, `x = 7/4``.`

`b,` `(-5)/6 + (-1)/6 : x = 2`

`->``(-1)/6 : x = 2 - (-5)/6`

`->``(-1)/6 : x = 17/6`

`->``x = (-1)/6 : 17/6`

`->``x = (-1)/17`

Vậy, `x = (-1)/17``.`

`c,` `(-7)/12 - 3/5 - x = 3/4`

`->``-x = 3/4 + 7/12 + 3/5`

`->``-x = 29/15`

`->``x = (-29)/15`

Vậy, `x = (-29)/15``.`