Câu 1:
`x^2 + 3xy - 4 + 6y`
`=(x^2 - 4) + (3xy + 6y)`
`=(x - 2)(x + 2) + 3y(x + 2)`
`=(x + 2)(x - 2 + 3y)`
Câu 2:
a.
`(x + 2)(x - 3) - x^2 + 5x = 18`
`⇔x^2 - 3x + 2x - 6 - x^2 + 5x = 18`
`⇔4x - 6 = 18`
`⇔4x = 24`
`⇔x = 6`
Vậy `x = 6`
b.
`3x - 9 - 2x(x - 3) = 0`
`⇔3(x - 3) - 2x(x - 3) = 0`
`⇔(x - 3)(3 - 2x) = 0`
`⇔`\(\left[ \begin{array}{l}x-3=0\\3-2x=0\end{array} \right.\)
`⇔`\(\left[ \begin{array}{l}x=3\\x=\dfrac{-3}{2}\end{array} \right.\)
Vậy `x = {-3/2; 3}`
