问题
解答题
已知a=2+
|
答案
原式=[
-3a(a-1) (a+1)(a-1)
]•a(a+1) (a+1)(a-1) (a+1)(a-1) a
=
•3a2-3a-a2-a (a+1)(a-1) (a+1)(a-1) a
=
•2a2-4a (a+1)(a-1) (a+1)(a-1) a
=
•2a(a-2) (a+1)(a-1) (a+1)(a-1) a
=2a-4，（4分）
当a=2+
时，原式=2（2+2
）-4=22
．（7分）2