问题 解答题
f(x)=
4x
4x+a
,且f(x)的图象过点
1
2
1
2
 )

(1)求f(x)表达式;
(2)计算f(x)+f(1-x);
(3)试求f(
1
2007
)+f(
2
2007
)+f(
3
2007
)+…
+f(
2005
2007
)+f(
2006
2007
)
的值.
答案

(1)∵f(x)=

4x
4x+a
过点
1
2
1
2
 )

f(

1
2
)=
4
1
2
4
1
2
+a
=
2
2+a
=
1
2
,解得a=2∴f(x)=
4x
4x+2

(2)f(x)+f(1-x)=

4x
4x+2
+
41-x
41-x+2
=
4x(41-x+2)+41-x(4x+2)
(4x+2)(41-x+2)
=
8+2•4x+2•41-x
8+2•4x+2•41-x
=1

(3)∵f(x)+f(1-x)=1

f(

1
2007
)+f(
2006
2007
)
=f(
2
2007
)+
f(
2005
2007
)
=…=f(
1002
2007
)+
f(
1005
2007
)
=f(
1003
2007
)
+f(
1004
2007
)
=1

f(

1
2007
)+f(
2
2007
)+f(
3
2007
)++f(
2005
2007
)+f(
2006
2007
)
=1003

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