Xét :`x^2 +4x+4=0`
`=>x^2 +2x+2x+4=0`
`=>(x^2 +2x)+(2x+4)=0`
`=>x(x+2)+2(x+2)=0`
`=>(x+2)(x+2)=0`
`=>(x+2)^2=0`
`=>x+2=0`
`=>x=-2`
Vậy đa thức có nghiệm `x=-2`
` x^2 + 4x + 4`
` x^2 + 4x + 4 =0`
`( x^2 + 2x) + ( 2x + 4) = 0`
` (x + 2).(x+2) = 0`
` (x+2)^2 = 0`
`=> x = -2`
Vậy....
\(x^2+4x+4=0\)
\(\Leftrightarrow x^2+2x+2x+4=0\)
\(\Leftrightarrow x\left(x+2\right)+2\left(x+2\right)=0\)
\(\Leftrightarrow\left(x+2\right)^2=0\)
\(\Leftrightarrow x+2=0\Leftrightarrow x=-2\)