1/2×5+1/5×8+1/8×11+…+1/2006×2009+1/2009×2012.
问题描述:
+1 2×5
+1 5×8
+…+1 8×11
+1 2006×2009
. 1 2009×2012
答
+1 2×5
+1 5×8
+…+1 8×11
+1 2006×2009
1 2009×2012
=
×(1 3
-1 2
+1 5
-1 5
+1 8
-1 8
+…+1 11
-1 2006
+1 2009
-1 2009
)1 2012
=
×(1 3
-1 2
)1 2012
=
×1 3
1005 2012
=
.335 2012