`(2x+1)^2=9`

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

`=>[(2x+1=3),(2x+1=-3):}`

`=>[(2x=2),(2x=-4):}`

`=>[(x=1),(x=-2):}`

Vậy `x=1` hoặc `x=-2`

`x^2+4x+4=0`

`⇔x^2+2.x.2+2^2=0`

`⇔(x+2)^2=0`

`⇔x+2=0⇔x=−2`

Vậy `x=-2`.

Văn em rất kém nma em sẽ cố viết :V

Thì xét 2 trường hợp á anh :v

`(x-1/2)^2`

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

`=x^2-x+1/4`

Hằng đẳng thức:`(a-b)^2=a^2-2ab+b^2`

Mất dấu nên xét 2 th.

TH1

`x^2-4x+4=0`

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

`<=>(x-2)^2=0`

`<=>x-2=0`

`<=>x=2`

`=>S={2}`

TH2

`x^2+4x+4=0`

`<=>x^2+2.x.2+2^2=0`

`<=>(x+2)^2=0`

`<=>x+2=0`

`<=>x=-2`

`=>S={-2}`

`0,125=125/1000=(125)/(125.8)=1/8`

`c) (x+5)(x^2 –5x +25) – (x – 7) = x^3`
`<=>x^3-125-x+7=x^3`
`<=>x^3-x-118=x^3`
`<=>-x-118=0`
`<=>-x=118<=>x=-118`
`d) (x+2)(x^2 – 2x + 4) – x(x^2 + 2) = 4 `
`<=>x^3+8-x^3-2x=4`
`<=>8-2x=4`
`<=>2x=4<=>x=2`