9n²-4m²-1+4m=9n²-(4m²-4m+1)=9n²-(2m-1)²=(3n+2m-1)(3n-2m+1)（x²-3x)²-8(x²-3x)-20=[(x²-3x)-10][(x²-3x)+2]=(x²-3x-10)(x²-3x+2)=(x-5)(x+2)(...