题目内容
先化简,再求值:
(1)(a-
)•
,其中a=1,-3<b<
且b为整数;
(2)
÷(m+2-
),其中m是方程x2+3x-1=0的根.
(3)化简分式(
-
)÷
,并从-1≤x≤3中选一个你认为合适的整数x代入求值.
(1)(a-
2ab-b2 |
a |
a2+ab |
a2-b2 |
3 |
(2)
m-3 |
3m2-6m |
5 |
m-2 |
(3)化简分式(
x |
x-1 |
x |
x2-1 |
x2-x |
x2-2x+1 |
(1)原式=
•
=
•
=a-b;
∵a2-b2≠0,
∴当a=1时,b≠±1.
①a=1,b=-2时,原式=1+2=3;
②a=1,b=0时,原式=1-0=1;
(2)原式=
÷(
-
)
=
÷
=
•
=
=
;
(3)原式=
•
=
,
当x=2时,原式=
=
.
a2-2ab+b2 |
a |
a(a+b) |
(a-b)(a+b) |
=
(a-b)2 |
a |
a(a+b) |
(a-b)(a+b) |
=a-b;
∵a2-b2≠0,
∴当a=1时,b≠±1.
①a=1,b=-2时,原式=1+2=3;
②a=1,b=0时,原式=1-0=1;
(2)原式=
m-3 |
3m(m-2) |
m2-4 |
m-2 |
5 |
m-2 |
=
m-3 |
3m(m-2) |
(m-3)(m+3) |
m-2 |
=
m-3 |
3m(m-2) |
m-2 |
(m-3)(m+3) |
=
1 |
3(m2+3m) |
=
1 |
3 |
(3)原式=
x2+x-x |
(x-1)(x+1) |
(x-1)2 |
x(x-1) |
=
x |
x+1 |
当x=2时,原式=
2 |
2+1 |
2 |
3 |
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