(1)原式=(x+5y)(x-5y);(2)原式=(5n-2m)(5n+2m);(3)原式=(a+b-2a)(a+b+2a)=(b-a)(3a+b);(4)原式=(a2+1)(a2-1)=(a2+1)(a+1)(a-1);(5)原式=(3m+3n-m+n)(3m+3n+m-n)=(2m+4n)(4m+2n)=4(m+2n)(2m+n);(6)原式=m(x2-4y2)=m(x-2y)(x+2y).