问题 解答题
如果有理数a,b满足|ab-2|+(1-b)2=0,试求
1
ab
+
1
(a+1)(b+1)
+
1
(a+2)(b+2)
+…+
1
(a+2007)(b+2007)
的值.
答案

∵|ab-2|≥0,(1-b)2≥0,且|ab-2|+(1-b)2=0,

∴ab-2=0,且1-b=0,解得ab=2,且b=1,

把b=1代入ab=2中,解得a=2,

1
ab
+
1
(a+1)(b+1)
+
1
(a+2)(b+2)
+…+
1
(a+2007)(b+2007)

=

1
2
+
1
3×2
+
1
4×3
+…+
1
2009×2008

=(1-

1
2
)+(
1
2
-
1
3
)+(
1
3
-
1
4
)+…+(
1
2008
-
1
2009

=1-

1
2
+
1
2
-
1
3
+
1
3
-
1
4
+…+
1
2008
-
1
2009

=1-

1
2009

=

2008
2009

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