9a²-四分之一b²
9（m+n）²-（m-n）²
4（a-2b）²-9（2a+b)²
-16x的四次方+81y的四次方
p的四次方-1
3ax²-3ay的四次方

1.
9a^2-b^2/4=(3a)^2-(b/2)^2=(3a+b/2)(3a-b/2)
2.
9（m+n)^2-（m-n)^2=[3(m+n)]^2-(m-n)^2=[3(m+n)+(m-n)][3(m+n)-(m-n)]=(4m+2n)(2m+4n)=4(2m+n)(m+2n)
3.
4(a-2b)^2-9(2a+b)^2=[2(a-2b)]^2-[3(2a+b)]^2=[2(a-2b)+3(2a+b)][2(a-2b)-3(2a+b)}=(8a+b)(-4a-7b)=-(8a+b)(4a+7b)
4.
-16x^4+81y^4=(9y^2)^2-(4x^2)^2=(9y^2+4x^2)(9y^2-4x^2)=(9y^2+4x^2)(3y+2x)(3y-2x)
5.
p^4-1=(p^2)^2-1^2=(p^2+1)(p^2-1)=(p^2+1)(p+1)(p-1)
6.
3ax^2-3ay^4=3a(x^2-y^4)=3a(x+y^2)(x-y^2)