a^2-b^2-2b-1=a^2-(b+1)^2=(a-b-1)(a+b+1)
=a^2-(b+1)^2=(a-b-1)(a+b+1)
原式=a^2-(b+1)^2=(a+b+1)(a-b-1)
a^2-b^2-2b-1=a^2-(b^2+2b+1)=a^2-(b+1)^2=(a+b+1)(a-b-1)
原式=A^2-(B^2+2B+1)=A^2-(B+1)^2=(A-B-1)(A+B+1)
