Question

因式分解（1）y^2-3y-4 （2）x^2+7xy-8y^2 （3）12m（x+y）^3-9n（x+y）^2

（4）（x^2-3x）^2-8（x^2-3x）-20.
要过程和结果

Answer 1

（1）y^2-3y-4 =(y-4)(y+1)
（2）x^2+7xy-8y^2 =(x+8y)(x-y)
（3）12m（x+y）^3-9n（x+y）^2=3(x+y)^2(4mx+4my-3n)
（4）（x^2-3x）^2-8（x^2-3x）-20
=(x^2-3x-10)(x^2-3x+2)
=((x-5)(x+2)(x-1)(x-2)

Answer 2

y²-3y-4
=(y-4)(y+1)
x²+7xy-8y²
=(x+8y)(x-y)
12m(x+y)^3-9n(x+y)²
=3(x+y)²[12m(x+y)-3n]
(x²-3x)²-8(x²-3x)-20
=(x²-3x-10)(x²-3x+2)
=(x-5)(x+2)(x-1)(x-2)