Đáp án:
Bài 1:
`a, -5/21 + (-2)/21 + 8/24`
`= (-5/21 - 2/21) + 1/3`
`= -7/21 + 1/3`
`= -1/3 + 1/3`
`= 0`
`b, -3/5 . 2/7 + (-3)/5 . 5/7 + 2 3/5`
`= -3/5(2/7 + 5/7) + 13/5`
`= -3/5 . 7/7 + 13/5`
`= -3/5 . 1 + 13/5`
`= -3/5 + 13/5`
`= 10/5 = 2`
`c, 75% - 1 1/2 + 0,5 : 5/12 - (-1/2)^2`
`= 75/100 - 3/2 + 1/2 : 5/12 - 1/4`
`= 3/4 - 3/2 + 1/2 . 12/5 - 1/4`
`= 3/4 - 1/4 - 3/2 + 6/5`
`= 1/2 - 3/2 + 6/5`
`= (1 - 3)/2 + 6/5`
`= -1 + 6/5 = -5/5 + 6/5`
`= 1/5`
Bài 2:
`a, 1 1/3 + (2/3).x = 5 1/3`
`(2/3)x = 5 1/3 - 1 1/3`
`(2/3)x = 4`
`x = 4 : 2/3 = 4. 3/2`
`x = 6`
`b, (x + 1/3)(3/4 - 2x) = 0`
`⇒ x + 1/3 = 0` hoặc `3/4 - 2x = 0`
`+ x + 1/3 = 0`
`⇒ x = 0 - 1/3`
`⇒ x = - 1/3`
`+ 3/4 - 2x = 0`
`⇒ 2x = 3/4 - 0`
`⇒ 2x = 3/4`
`⇒ x = 3/4 : 2 = 3/4 . 1/2`
`⇒ x = 3/8`
Vậy `x = -1/31` hoặc `x = 3/8`
`c, -4/5 x + 1 1/3 x = -1 1/3`
`-4/5 x + 4/3 x = -4/3`
`(-4/5 + 4/3)x = -4/3`
`(-12/15 + 20/15)x = -4/3`
`8/15 x = -4/3`
`x = -4/3 : 8/15`
`x = -4/3 . 15/8`
`x = - 5/2`
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