Câu`1:` `x² - 1/49 = 0`

`⇒ x² - (1/7)^2 = 0`

`⇒ (x - 1/7)(x + 1/7) = 0`

`⇒ x = 1/7 ; x = 1/7`

Vậy `x ∈ {1/7 ; -1/7}`

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Câu`2:` `x(x - 2) + x - 2 = 0`

`⇒ x(x - 2) + (x - 2) = 0`

`⇒ (x - 2) (x + 1) = 0`

`⇒ x = 2 ; x = -1`

Vậy `x ∈ {2 ; -1}`

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Câu`3:` `x³ - 1/4x = 0`

`⇒  x(x² - 1/4 ) = 0`

`⇒ x(x - 1/2)(x + 1/2) = 0`

`⇒ x = 0 ; x = 1/2 ; x = -1/2`

Vậy `x ∈ {0 ; 1/2 ; -1/2}`

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Câu`4:` `5x(x - 3) - x + 3 = 0`

`⇒ 5x(x - 3) - (x - 3) = 0`

`⇒ (x - 3) (5x - 1) = 0`

`⇒ x = 3 ; x = 1/5`

Vậy `x ∈ {3 ; 1/5}`

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Câu`5:` `(2x - 1)² - (x + 3)² = 0`

`⇒ [(2x - 1) - (x + 3)][(2x - 1) + (x + 3)]`

`⇒ (2x - 1 - x - 3)(2x - 1 + x + 3)`

`⇒ (x - 4)(3x + 2)`

`⇒ x = 4 ; x = -2/3`

Vậy `x ∈ {4 ; -2/3}`

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Câu`6:` `x²(x - 3) + 12 - 4x = 0`

`⇒ x²(x - 3) - 4x + 12 = 0`

`⇒ x²(x - 3) - 4(x - 3) = 0`

`⇒ (x - 3)(x² - 4) = 0`

`⇒ (x - 3)(x - 2)(x + 2) = 0`

`⇒ x = 3 ; x = 2 ; x = -2`

Vậy `x ∈ {3 ; 2 ; -2}`