问题 解答题
计算:
(1)
7a
3(a-4)
+
4a
3(4-a)

(2)
x2
x-1
-x-1

(3)
12
m2-9
+
2
3-m
+
1
m+3

(4)
x2
y-x
-
y2
y-x

(5)
a2
a+1
+1-a

(6)(
x+2
x2-2x
-
x-1
x2-4•x+4
)•
x
4-x
答案

(1)原式=

7a-4a
3(a-4)

=

a
a-4

(2)原式=

x2
x-1
-
(x+1)(x-1)
x-1

=

x2-x2+1
x-1

=

1
x-1

(3)

12
m2-9
-
2m+6
m2-9
+
m-3
m2-9

=

3-m
m2-9

=-

1
m+3

(4)原式=

x2-y2
y-x

=

(x-y)(x+y)
y-x

=-x-y;

(5)原式=

a2
a+1
+
1-a2
a+1

=

1
a+1

(6)原式=[

x+2
x(x-2)
-
x-1
(x-2)2
]•
x
4-x

=[

x2-4
x(x-2)2
-
x2-x
x(x-2)2
]•
x
4-x

=-

1
x2-4x+4

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