问题
解答题
| 计算． （1）a+b+
（2）(x+1-
（3）(2+
|
答案
（1）a+b+2b2 a-b
=
+(a+b)(a-b) a-b 2b2 a-b
=
；a2+b2 a-b
（2）(x+1-
)÷3 x-1 x+2 2x-2
=[
-(x+1)(x-1) x-1
]×3 x-1 2(x-1) x+2
=
×(x+2)(x-2) x-1 2(x-1) x+2
=2x-4；
（3）(2+
-1 a-1
)÷(a-1 a+1
)，a 1-a2
=[
+2(a+1)(a-1) (a+1)(a-1)
-(a+1) (a-1)(a+1)
]÷[a-1 (a+1)(a-1)
+a(a+1)(a-1) (a+1)(a-1)
]a (a+1)(a-1)
=
×2a2 (a+1)(a-1) (a+1)(a-1) a3
=
，2 a
把a=2代入原式得：原式=
=1．2 a