(a-3)²-(2a-b)²
=（a-3+2a-b）（a-3-2a+b）平方差公式
=（3a-b-3）(-a+b-3)9(x+y+z)平方-（x-y-z）平方分解因式9(x+y+z)²-（x-y-z）²=[3(x+y+z)]²-（x-y-z）²=(3x+3y+3z)²-（x-y-z）²=(3x+3y+3z+x-y-z)(3x+3y+3z-x+y+z)=(4x+2y+2z)(2x+4y+4z)=4(2x+y+z)(x+2y+2z)