Tìm x biết a. (x+1)^3-(x-1)^3-6x^2+2x=0 b.(2x-1)^3-2x(2x+1)^2=5x-20x^2

`a,`

`(x + 1) ^ 3 - (x - 1) ^ 3 - 6x ^ 2 + 2x = 0`

`<=>(x + 1 - x + 1) .[(x+1)^ 2 +(x+1).(x-1)+(x-1)^ 2 ] - 6x ^ 2 + 2x = 0`

`<=>2. (x ^ 2 + 2x + 1 + x ^ 2 - 1 + x ^ 2 - 2x + 1) - 6x ^ 2+2x = 0`

`<=>2. (3x ^ 2 + 1) - 6x ^ 2 + 2x = 0`

`<=>6x ^ 2 + 2 - 6x ^ 2 + 2x = 0`

`<=>2x + 2 = 0`

`=>x = - 1`

`b,`

`(2x-1)^ 3 -2x. (2x + 1) ^ 2 = 5x - 20x ^ 2`

`<=>8x ^ 3 - 3.4x ^ 2 + 3.2x - 1 -2x.(4x^ 2 +4x+1)= 5x - 20x ^ 2`

`<=>8x ^ 3 - 12x ^ 2 + 6x - 1 - 8x ^ 3 - 8x ^ 2 - 2x= 5x- 20x ^ 2`

`<=>- 20x ^ 2 + 4x - 1 = 5x - 20x ^ 2`

`<=>- x - 1 = 0`

`=>x = - 1`

`@`ngocnhuyle