Câu 1:
`(a+b)^2-4(a-b)^2`
`=(a+b)^2-[2(a-b)]^2`
`=(a+b-2a+2b)(a+b+2a-2b)`
`=(-a+3b)(3a-b)`
Câu 2:
`5x(x-2)=x-2`
`⇒5x(x-2)-(x-2)=0`
`⇒(5x-1)(x-2)=0`
`⇒` \(\left[ \begin{array}{l}5x-1=0\\x-2=0\end{array} \right.\)
`⇒` \(\left[ \begin{array}{l}5x=1\\x=0+2\end{array} \right.\)
`⇒` \(\left[ \begin{array}{l}x=1/5\\x=2\end{array} \right.\)