①x(x^2+1)-y(y^2+1)
=x³-y³+x-y
=(x-y)(x²+xy+y²)+(x-y)
=(x-y)(x²+xy+y²+1)
②a^2-b^2+4a+2b+3
=(a+2)²-(b-1)²
=(a+2+b-1)(a+2-b+1)
=(a+b+1)(a-b+3)