`#Sad`
`(x-1)^2-5 = (x+2)(x-2)-x(x-1)`
`⇔ x^2-2x+1-5 = x^2-4-x^2+x`
`⇔ x^2-2x-4-x+4 = 0`
`⇔ x^2-3x = 0`
`⇔ x(x-3) = 0`
`⇔` \(\left[ \begin{array}{l}x=0\\x-3=0\end{array} \right.\)
`⇔` \(\left[ \begin{array}{l}x=0\\x=3\end{array} \right.\)
`\text{Vậy}` `x=0` `\text{hoặc}` `x=3`
`\text{Áp dụng:}`
`+)` `A^2-B^2 = (A-B)(A+B)`
`+)` `(A-B)^2 = A^2-2AB+B^2`