Đáp án+Giải thích các bước giải:
a) `720 : [41 - (2x - 5)] = 2^3 . 5`
`⇒ 720 : [41 - (2x - 5)] = 8 . 5`
`⇒ 720 : [41 - (2x - 5)] = 40`
`⇒ 41 - (2x - 5) = 720 : 40`
`⇒ 41 - (2x - 5) = 18`
`⇒ 2x - 5 = 41 - 18`
`⇒ 2x - 5 = 23`
`⇒ 2x = 23 + 5`
`⇒ 2x = 28`
`⇒ x = 28 : 2`
`⇒ x = 14`
Vậy `x = 14`
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b) `6(x + 11) - 7(2 - x) = 26`
`⇒ 6x + 66 - 7(2 - x) = 26`
`⇒ 6x + 66 - 7(-x + 2) = 26`
`⇒ 6x + 66 - 7x - 14 = 26`
`⇒ 6x + 52 + 7x = 26`
`⇒ 13x + 52 = 26`
`⇒ 13x + 52 - 52 = 26 - 52`
`⇒ 13x = -26`
`⇒ x = -26 : 13`
`⇒ x = -2`
Vậy `x = -2`
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c) `2016 : [25 - (3x + 2)] = 3^2 . 7`
`⇒ 2016 : [25 - (3x + 2)] = 9 . 7`
`⇒ 2016 : [25 - (3x + 2)] = 63`
`⇒ 25 - (3x + 2) = 2016 : 63`
`⇒ 25 - (3x + 2) = 32`
`⇒ 3x + 2 = 25 - 32`
`⇒ 3x + 2 = -7`
`⇒ 3x = (-7) - 2`
`⇒ 3x = -9`
`⇒ x = -9 : 3`
`⇒ x = -3`
Vậy `x = -3`
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d) `13/x - 1 + 5/2x - 2 = 6/3x - 3`
`⇒ (2.13)/(2(x-1)) + 5/2x = 6/(3x - 3)`
`⇒ 26/(2x) - 2 + 5/(2x) - 2 = 6/(3x-3)`
`⇒ (26+5)/2x - 2 = 6/(3x-3)`
`⇒ 31/(2x) - 2 = 6/(3x-3)`
`⇒ 31/(2x-2) = (6:3)/((3x-3):3)`
`⇒ 31/(2x-2) = 2/(x-1)`
`⇒ 31/(2x-2)=4/(2x-2)`
`⇒ 31/(2x-2) - 4/(2x-2) = 0`
`⇒ 27/(2x-2) = 0`
`⇒ 0. 2x-2 = 27`
`⇒ 0 = 27`
Vậy `x ∈ ∅` hay `x = {}`