200820082009×12008;11×9+19×11+111×13+…119×21.-数学

题文

2008
2008
2009
×
1
2008
1
1×9
+
1
9×11
+
1
11×13
+…
1
19×21
题型:解答题  难度:中档

答案

(3)2668
2668
2669
×
3
2668

=(2668+
2668
2669
)×
3
2668

=2668×
3
2668
+
2668
2669
×
3
2668

=3+
3
2669

=3
3
2669


(2)
3
7×9
+
3
9×33
+
3
33×33
+…+
3
39×23

=
3
2
×(
3
7
-
3
9
+
3
9
-
3
33
+…+
3
39
-
3
23

=
3
2
×(
3
7