phân tích thành nhân tử a)x² + 4x b)5(x-y)-y(x-y) c)x² - 2x + 1 - y² tìm x biết a) 5(x-1)+10=0 b)2x(x+5)-x-5=0

`a)x^2+4x`

`=x(x+4)`

`b)5(x-y)-y(x-y)`

`=(5-y)(x-y)`

`c)x^2+2x+1-y^2`

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

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

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

`=(x+1+y)(x+1-y)`

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`a)5(x-1)+10=0`

`⇒5x-5+10=0`

`⇒5x+5=0`

`⇒5x=-5`

`⇒x=-1`

Vậy `x=-1`

`b)2x(x+5)-x-5=0`

`⇒2x(x+5)-(x+5)=0`

`⇒(2x-1)(x+5)=0`

`⇒` \(\left[ \begin{array}{l}2x-1=0\\x+5=0\end{array} \right.\) 

`⇒` \(\left[ \begin{array}{l}x=\frac{1}{2}\\x=-5\end{array} \right.\)  

Vậy `x∈{1/2;-5}`