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`a, 3x( x - 2 ) - x( 1 + 3x ) = 14`
`<=> 3x^2 - 6x - x - 3x^2 = 14`
`<=> -7x = 14`
`<=> x=-2`
Vậy `x=-2`
`b, (3x+1)^2 + (5x-2)^2 = 34(x+2)(x-2)` (Sửa đề tí nhé)
`<=> 9x^2 + 6x + 1 + 25x^2 - 20x + 4 - 34(x^2 - 4) = 0`
`<=> 9x^2 + 6x + 1 + 25x^2 - 20x + 4 - 34x^2 + 136 = 0`
`<=> -14x + 141 = 0`
`<=> -14x = -141`
`<=> x= 141/14`
Vậy `x=141/14`
`c, x^3 + 3x^2 + 3x + 1 = 125`
`<=> x^3 + 3*x^2* 1 + 3* x * 1^2 + 1^3 = 5^3`
`<=> (x+1)^3 = 5^3`
`<=> x+1 = 5`
`<=> x=4`
Vậy `x=4`