12道十字相乘因式分解题1.x²-xy-2y²2.x²+6xy+8y²3.2x&

1.x²-xy-2y²=(x+y)(x-2y)
2.x²+6xy+8y²=(x+2y)(x+4y)
3.2x²-xy-y²=(2x+y)(x-y)
4.4x²-xy-5y²=(4x-5y)(x+y)
5.abcx²+(a²b²+c²)x+abc=(abx+c)(cx+ab)
6.mnx²-(m²+n²)xy+mny²=(mx-ny)(nx-my)
7.(x²-2) ²-(x²-2)-2=[(x²-2)+1][(x²-2)-2]=(x²-1)(x²-4)=(x+1)(x-1)(x+2)(x-2)
8.(x²+4x) ²-x²-4x-20=(x²+4x)²-(x²+4x)-20=[(x²+4x)+4][(x²+4x)-5]=(x+2)²(x-1)(x+5)
9.(x+y)(x+y+2xy)+x²y²-1=(x+y)²+2xy(x+y)+(xy)²-1=(x+y+xy)²-1=(x+y+xy+1)(x+y+xy-1)
=(x+1)(y+1)(x+y+xy-1)
10.x²-3xy-10y²+x+9y-2=(x²-3xy-10y²)+x+9y-2=(x+2y)(x-5y)+2(x+2y)-(x-5y)-2
=(x+2y-1)(x-5y+2)
11.a²+ab-6b²+5a+35b-36=(a²+ab-6b²)+5a+35b-36=(a-2b)(a+3b)-4(a-2b)+9(a+3b)-36
=(a-2b+9)(a+3b-4)
12.x³-3x²+4=(x³+x²)-(4x²-4)=x²(x+1)-4(x+1)(x-1)=(x+1)(x²-4x+4)=(x+1)(x-2)²

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