分解因式：x2-y2-2y-1=______．
x2-y2-2y-1，
=x2-（y2+2y+1），
=x2-（y+1）2，
=（x+y+1）（x-y-1）．
把方程2y=y+7的两边都减去y得2y-y=y-y+7，整理得2y-y=7，这种变形叫______，根据______．
131. The magician said to the audience: “Ladies and gentlemen, before your very I will now make this rabbit disappear.”
A．eye
B．ear
C．head
D．Mouth
