a) \(x^2-y^2-2x-2y=\left(x-y\right)\left(x+y\right)-2\left(x+y\right)=\left(x+y\right)\left(x-y-2\right)\)
b) \(18m^2-36mn+18n^2-72p^2=18\left(m^2-2mn+n^2-4p^2\right)=18\left[\left(m-n\right)^2-4p^2\right]\\ =18\left(m-n+2p\right)\left(m-n-2p\right)\)
c) \(2x^2-5x+7=2x^2+2x-7x-7=2x\left(x+1\right)-7\left(x+1\right)=\left(x+1\right)\left(2x-7\right)\)
d) \(\left(x-1\right)\left(x-2\right)\left(x-3\right)\left(x-4\right)-24\)
\(=\left[\left(x-1\right)\left(x-4\right)\right]\left[\left(x-2\right)\left(\cdot x-3\right)\right]-24\)
\(=\left(x^2-5x+4\right)\left(x^2-5x+6\right)-24\)
Đặt \(x^2+5x+5=t\) pt trở thành:
\(\left(t-1\right)\left(t+1\right)-24=t^2-1-24=t^2-25=\left(t-5\right)\left(t+5\right)\)
Thay vào bên trên
