a^2 x^2+16ax+64=(ax)^2+16ax+64
=(ax+8)^2
应该是16（x-y)^2吧
25(x+y)^2-16(x-y)^2=(5(x+y))^2-(4(x-y))^2
=（9x+y)(x+9y)
x^2-6x+9-y^2=(x-3)^2-y^2
=(x-3+y)(x-3-y)
(a^2+b^2-1)^2-4a^2 b^2=(a^2+b^2-1)^2-(2ab)^2
=(a^2+b^2-1+2ab)(a^2+b^2-1-2ab)
=((a+b)^2-1)((a-b)^2-1)
=(a+b+1)(a+b-1)(a-b+1)(a-b-1)