问题
解答题
计算:1+3
|
答案
:1+3
+51 6
+71 12
+91 20
+111 30
+131 42
+151 56
+171 72
+191 90
,1 110
=(1+19)+(3+17)+(5+15)+(7+13)+(9+11)+
+1 2×3
+…+1 3×4
+1 9×10
,1 10×11
=(1+19)+(3+17)+(5+15)+(7+13)+(9+11)+(
-1 2
+1 3
-1 3
+…+1 4
-1 9
+1 10
-1 10
),1 11
=20+20+20+20+20+(
-1 2
),1 11
=100
.9 22