1)
x²-3ax-6ab-4b²= (x+2b)(x-2b)-3a(x+2b)=(x+2b)(x-2b-3a)
2)怀疑是2xy.
1-x²+4xy-y²=1+-(x²-2xy+y²)=1-(x-y)²=(1+x-y)(1-x+y)