问题
选择题
设s=
则与s最接近的整数是( )
|
答案
∵n为任意的正整数,
∴
=1+
+1 n2 1 (n+1)2 n2(n+1)2+n2+(n+1)2 [n(n+1)]2
=
=[n(n+1)]2+2n(n+1)+1 [n(n+1)]2
=(n2+n+1)2 [n(n+1)]2
=1+n2+n+1 n(n+1)
,1 n(n+1)
∴s=(1+
)+(1+1 1×2
)+(1+1 2×3
)+…+(1+1 3×4
)1 2008×2009
=2008+(
+1 1×2
+1 2×3
+…+1 3×4 1 2008×2009
=2008+(1-
)+(1 2
-1 2
)+(1 3
-1 3
)+…+(1 4
-1 2008
)1 2009
=2009-
.1 2009
因此与s最接近的整数是2009.
故选A.