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.
······································································································ 2分
········································································································· 3分
．···················································································································· 4分
时，原式
．······································································ 6分
=
时，4a2+2=4×(
代入上式得
·························································· 4分
·························································································································· 6分
，
时，
···································································································· 8分
57. 
58. 
59. 
60. 
或
61. 
62. 
63. 
64. (a+2)(a-2) 65. 
66. 
67. 