（x+5）²-（5x+1）²=(x+5+5x+1)(x+5-5x-1)=(6x+6)(-4x+4)=-24(x+1)(x-1)
4（x-6）²-（3+x）²=(2x-12)²-(3+x)²=(2x-12+3+x)(2x-12-3-x)=(3x-9)(x-15)=3(x-3)(x-15)
9（2x-3）²-（3x）²=(6x-9)²-(3x)²=(6x-9+3x)(6x-9-3x)=(9x-9)(3x-9)=27(x-1)(x-3)