1.xy-2x+3y-6
=y(x+3)-2(x+3)=(x+3)(y-2)
2.5axy-5bxy+2ax-2bx+10cxy+4cx
=5xy(a-b)+2x(a-b)+2cx(5y-2)
=(a-b)(5xy+2x)+2cx(5y+2)
=x(a-b)(5y+2)+2cx(5y+2)
=x(5y+2)(a-b+2c)
题目最后应该多了个平方
3. 6x²-7xy-3y²-x+7y-2
=(2x-3y)(3x+y)-2(2x-3y)+(3x+y)-2
=(2x-3y+1)(3x+y-2)
化简（a-2b+3c)³
=(a-2b)³+3(a-2b)²*3c+3(a-2b)(3c)²+(3c)³
=a³-6a²b+12ab²-8b³+9a²c-36abc+36b²c+27ac²-54bc²+27c³