1.（2x+y）^2-（x+2y）^2
=(2x+y+x+2y)(2x+y-x-2y)
=(3x+3y)(x-y)
=3(x+y)(x-y)
2.（p-4）（p+1）+3p
=p²-3p-4+3p
=p²-4
=(p+2)(p-2)
3.3ax^2-3ay2
=3a(x²-y²)
=3a(x+y)(x-y)
4.12a（x^2+y^2）-18b（x^2+y^2）
=6(x²+y²)(2a-3b)
5.-a^5+a
=-a(a^4-1)
=-a(a²+1)(a²-1）
=-a(a²+1)(a+1)(a-1)
6.3（m+n）^2-27n^2
=3[(m+n)²-(3n)²]
=3(m+n+3n)(m+n-3n)
=3(m+4n)(m-2n)
7.25（x+y）^2-9（x-y）^2
=[5(x+y)]²-[3(x-y)]²
=(5x+5y+3x-3y)(5x+5y-3x+3y)
=(8x+2y)(2x+8y)
=8(4x+y)(x+4y)
问题补充：
还有一个 先分解因式,再计算 πR1^2+πR2^2+πR3^2,其中R1=4 R2=8 R3=10 π取3.14
πR1^2+πR2^2+πR3^2
=π(R1^2+R2^2+R3^2)
=3.14(16+64+100)
=565.2