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`b, 2x(5x+3) + (4-2x)5x=8`
`<=> 10x^2+6x+20x-10x^2=8`
`<=> 26x=8`
`<=> x=4/13`
Vậy `x=4/13`
`c, 3x^3 - 4(x+2) = 4x(x^2-1)`
`<=> 3x^3 - 4x - 8 = 4x^3 - 4x`
`<=> 3x^3 -4x^3 - 4x + 4x = 8`
`<=> -x^3 = 8`
`<=> -x^3=-(-2)^3`
`<=> x= -2`
Vậy `x=-2`