观察下列等式 1+3=
1+3+5=
1+3+5+7=
1+3+5+7+9=
‥‥‥ (1)按规律填空:1+3+5+7+…+99=______; (2)计算1+3
|
(1)1+3+5+7+9+…+99
=(
)21+99 2
=502
=2500;
(2)原式=1+3+5+7+9+11+(
+1 6
+1 12
+1 20
+1 30
)1 42
=(
)2+(1+11 2
-1 2
+1 3
-1 3
+1 4
-1 4
+1 5
-1 5
+1 6
-1 6
)1 7
=36+(
-1 2
)1 7
=36
.5 14