`(2x+1)^2-4(x+2)^2=9`
`⇔ 4x^2 + 4x + 1 - 4x^2 - 16x - 16 = 9`
`⇔ (4x^2-4x^2) - (16x-4x) = 9 + 16 - 1`
`⇔ -12x = 24`
`⇔ x = -2`
Vậy `S = {-2}`
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`(x+3)^2 - (x-4)(x+8) = 1`
`⇔ x^2 + 6x + 9 - x^2 - 4x + 32 = 1`
`⇔ (x^2-x^2) + (6x-4x) = 1 - 32 - 9`
`⇔ 2x = -40`
`⇔ x = -20`
Vậy `S = {-20}`
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`3(x+2)^2 + (2x-1)^2 - 7(x+3)(x-3) = 36`
`⇔ 3x^2 + 12x + 12 + 4x^2 - 4x + 1 - 7x^2 + 63 = 36`
`⇔ (7x^2-3x^2-4x^2) + (12x-4x) = 36 - 63 - 1 - 12`
`⇔ 8x = -40`
`⇔ x = -5`
Vậy `S = {-5}`
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`(5x+1)^2 + (5x+3)(3-5x) = 30`
`⇔ 25x^2 + 10x + 1 + 9 -25x^2 = 30`
`⇔ (25x^2-25x^2) + 10x = 30 - 9 - 1`
`⇔ 10x = 20`
`⇔ x = 2`
Vậy `S = {2}`
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`(2x+1)^2+(2x-1)^2=10+8(x-1)(x+1)`
`⇔ 4x^2 + 4x + 1 + 4x^2 - 4x + 1 = 10 + 8x^2 - 8`
`⇔ (4x^2+4x^2) + (4x-4x) + (1+1) = 8x^2 + 2`
`⇔ 8x^2 + 2 = 8x^2 + 2`
`⇔ 0x = 0` (luôn đúng `∀x`)
Vậy `S = RR`
