tìm x 3x^2 - 6x =0 3x^3 - x =0 (x-1)^2 = x+2 (3x - 5)^2 - (x+1)^2 =0 (5x - 4)^2 -49x^2 =0

`a)`

`3x^2 - 6x=  0`

`=> 3x (x-2) = 0`

`=>x=0` hoặc `x-2=0`

`+)x=0`

`+)x-2=0=>x=2`

Vậy `x \in {0;2}`

`b)`

`3x^3  -x = 0`

`=> x (3x^2 - 1) = 0`

`=>x=0` hoặc `3x^2 -1=0`

`+)x=0`

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

`=> 3x^2 =1`

`=> x^2=  1/3`

`=> x = +-\sqrt{1/3}`

Vậy `x \in {0; \sqrt{1/3} ; - \sqrt{1/3} }`

`c)`

`(x-1)^2 = x+2`

`=> x^2 - 2x + 1 = x+2`

`=> x^2 - 2x + 1 - x - 2=0`

`=> x^2 - 3x - 1 = 0`

`=> (x^2 - 3x + 9/4) - 13/4 = 0`

`=> (x-3/2)^2 = 13/4`

`=> x-3/2 = \sqrt{13/4}` hoặc `x-3/2=- \sqrt{13/4}`

`+)x-3/2= \sqrt{13/4}`

`=> x = (\sqrt{13} + 3)/2`

`+)x-3/2= -\sqrt{13/4}`

`=> x = (-\sqrt{13} + 3)/2`

Vậy `x \in { (\sqrt{13} + 3)/2 ; (-\sqrt{13} + 3)/2 }`

`d)`

`(3x-5)^2-  (x+1)^2=0`

`=> [ (3x-5) + (x+1)] . [ (3x-5) - (x+1)] =0`

`=> (3x-5+x+1)(3x-5-x-1)=0`

`=> (4x - 4)(2x-6)=0`

`=> 4x-4=0` hoặc `2x-6=0`

`+) 4x - 4 = 0`

`=> 4x=4`

`=>x=1`

`+)2x-6=0`

`=> 2x=6`

`=>x=3`

Vậy `x \in {1;3}`

`e)`

`(5x-4)^2 - 49x^2 =0`

`=> (5x-4)^2  - (7x)^2 = 0`

`=> (5x-4-7x)(5x-4+7x)=0`

`=> (-2x-4)(12x-4)=0`

`=> -2x-4=0` hoặc `12x-4=0`

`+)-2x-4=0`

`=> -2x = 4`

`=> x= -2`

`+)12x-4=0`

`=> 12x=4`

`=>x=1/3`

Vậy `x \in {-2  ; 1/3}`