8. 解：

······································································································ 2分

········································································································· 3分

．···················································································································· 4分

当时，原式．······································································ 6分

7. 解：(以下给出三种选择方案，其他方案从略)　

　 　解答一：Y + Z =(3a²+3ab)+ (a²+ab)

　　　　　　　 =4a²+4ab　　　

　　　　　　　 =4a(a+b)．　　　

　 　解答二： X- Z = (2a²+3ab+b²)-(a²+ab)

　　　　　　 　=a²+2ab+b²=(a+b)²．　　　

解答三：Y- X=(3a²+3ab)- (2a²+3ab+b²)

=a²- b² =(a+b)(a-b)．　

6. 解：原式==

5.

解：原式=4a²+4a+1-4a-2+3……………………………………………………3分

　　　　 =4a²+2.…………………………………………………………………4分

当a=时，4a²+2=4×()²+2=10. …………………………………6分

4.

解：解：原式

　　 将代入上式得

　　 原式

3. 解：原式＝

　　　　　　 ＝

　　 　　　　　＝

2. 解：原式·························································· 4分

·························································································································· 6分

当，时，

原式···································································································· 8分

1.

68. (x-1)²

56. 　　57. 　　58. 　　59. 　　60. 或　 　　　61. 　　62. 　　63. 　　64. (a+2)(a-2)　 65. 　　66. 　　67.