bài 1)
`1) A = -2/4 + 2/7 - 5/28`
`= -14/28 + 8/28- 5/28`
`=\frac{-14 + 8 - 5}{28}`
`= -11/28`
`2) B = ( 5/7 . 0,6 - 5 : 3 1/2) . 40% - 1,4 . (-2)³`
`= ( 5/7 . 3/5 - 5 . 2/7 ) . 2/5 - 7/5 . (-8)`
`= ( 3/7 - 10/7) . 2/5 - (-56/5)`
`= -1 . 2/5 + 56/5`
`= -2/5 + 56/5`
`= 54/5`
Bài 2)
`a) x -2/3= 7/12`
`x = 7/12 + 2/3`
`x = 7/12 + 8/12`
`x = 5/4`
`b) 1/2 . x + 3/5 . x - 2 = 3`
`(1/2+ 3/5) . x = 3+2`
`( 5/10 + 6/10) . x = 5`
`11/10 . x = 5`
`x = 5 : 11/10`
`x = 50/11`
