解:x ² - 6 x y + 8 y ²
= x ² +(- 4 - 2)x y + (- 4 y)(- 2 y)
= (x - 4 y)(x - 2 y)
参考公式:
十字相乘法:x ² + (p + q)x + p q = (x + p)(x + q)
原式=(x-2y)(x-4y)
x^2-6xy+8y^2
=x^2-2xy-4xy+8y^2
=x(x-2y)-4y(x-2y)
=(x-2y)(x-4y)
x^2-2xy-4xy+8y^2=x(x-2y)-4y(x-2y)=(x-4y)(x-2y)