12x²-11xy-15y²=(4x+3y)(3x-5y)
-20xy+64x²+x² (题目?) →64x²-20xy+y²=(16x-y)(4x-y)
4x²+24xy+27y²=(2x+3y)(2x+9y)
xy-1-x+y=x(y-1)-(y-1)=(y-1)(x-1)
m²-n²+2n-1=m²-(n²-2n+1)=m²-(n-1)²=(m+n-1)(m-n+1)
x²+y²-9z²-1-2xy-6z=x²-2xy+y²-(9z²+6z+1)=(x-y)²-(3z+1)²=(x-y+3z+1)(x-y-3z-1)