1.
a^3-b^3+2a-2b
=a*a*a-b*b*b+2a-2b
=(a-b)(a^2+b^2+ab+2)
2.
25a^4-x^2-2x-1
=25*a*a*a*a-x*x-2x-1
=(5a^2+x+1)(5a^2-x-1)
3.
y^3+x^3+y^2-xy+x^2
=y*y*y+x*x*x+y*y-x*y+x*x
=(x+y+1)(x^2-xy+y^2)
4.
3m^4-3+7m^y+7y
=3*m*m*m*m-3+7m*m*m*m……(y个m)+7y