Đáp án:
`a,`
`(2/5 - x) ÷ 1 1/3 + 1/2 = -4`
`-> (2/5 - x) ÷ 4/3 = -4 - 1/2`
`-> (2/5 - x) ÷ 4/3 =(-9)/2`
`-> 2/5 - x= (-9)/2 × 4/3`
`-> 2/5 - x = -6`
`-> x = 2/5 - (-6)`
`->x =32/5`
Vậy `x = 32/5`
`b,`
`(-3 + 3/x - 1/3) ÷ (1 + 2/5 + 2/3) = 5/4`
`-> (3 + 3/x - 1/3) ÷ 31/15 = 5/4`
`-> 3 + 3/x - 1/3 = 5/4 × 31/15`
`-> 3 + 3/x - 1/3 = 31/12`
`-> 3/x + 8/3 = 31/12`
`-> 3/x = 31/12 - 8/3`
`-> 3/x =(-1)/12`
`-> -x = 3 × 12`
`-> -x = 36`
`-> x = -36`
Vậy `x = -36`
`c,`
`(-3x)/4 × (1/4 + 2/7) = 0`
`-> (-3x)/4 × 15/28 = 0`
`-> (-3x)/4 = 0 ÷ 15/28`
`-> (-3x)/4 = 0`
`-> -3x = 4 × 0`
`-> -3x = 0`
`-> x = 0 ÷ (-3)`
`-> x=0`
Vậy `x=0`
`d,`
`3 - (1-1/2)/(1 + 1/x) = 2 2/3`
`-> 3 - (1/2)/(1 + 1/x) = 8/3`
`-> (1/2)/(1+1/x)=3 - 8/3`
`-> (1/2)/(1+1/x)=1/3`
`-> 1/2 = (1 + 1/x) × 1/3`
`-> 1 + 1/x = 1/2 ÷ 1/3`
`-> 1 + 1/x=3/2`
`-> 1/x = 3/2 - 1`
`-> 1/x =1/2`
`-> x = 2`
Vậy `x=2`
`f,`
`(x -1)/65 + (x-3)/63 = (x-5)/61 + (x-7)/59`
`-> (x -1)/65 + (x-3)/63 - (x-5)/61 - (x-7)/59 = 0`
`-> ( (x-1)/65 - 1) + ( (x-3)/63 - 1) - ( (x-5)/61 - 1) - ( (x-7)/59- 1) = 0`
`-> ( (x-1)/65 - 65/65) + ( (x-3)/63 - 63/63) - ( (x-5)/61 - 61/61) - ( (x-7)/59 - 59/59) = 0`
`-> (x - 66)/65 + (x - 66)/63 - (x - 66)/61 - (x - 66)/59 = 0`
`-> (x - 66) (1/65 + 1/63 - 1/61 - 1/59) = 0`
`-> x - 66 = 0` (Vì `1/65 + 1/63 - 1/61 - 1/59 \ne 0`)
`-> x = 66`
Vậy `x = 66`
