1.a-1/16a^5
=a(1-1/16a^4)
=a(1-1/4a^2)(1+1/4a^2)
=a(1-1/2a)(1+1/2a)(1+1/4a^2)
2.1/27m-3m^5
=3m(1/81-m^4)
=3m(1/9-m^2)(1/9+m^2)
=3m(1/3-m)(1/3+m)(1/9+m^2)
3.a^2-b^2+a-b
=(a-b)(a+b)+a-b
=(a-b)(a+b+1)