计算:1+316+5112+7120+9130+11142+13156+15172+17190=______.-数学

题目简介

计算:1+316+5112+7120+9130+11142+13156+15172+17190=______.-数学

题目详情

计算:
1+3
1
6
+5
1
12
+7
1
20
+9
1
30
+11
1
42
+13
1
56
+15
1
72
+17
1
90
=______.
题型:解答题难度:中档来源:不详

答案

1+3class="stub"1
6
+5class="stub"1
12
+7class="stub"1
20
+9class="stub"1
30
+11class="stub"1
42
+13class="stub"1
56
+15class="stub"1
72
+17class="stub"1
90

=(1+3+5+7+9+11+13+15+17)+(class="stub"1
2×3
+class="stub"1
3×4
+class="stub"1
4×5
+class="stub"1
5×6
+class="stub"1
6×7
+
class="stub"1
7×8
+class="stub"1
8×9
+class="stub"1
9×10
),
=class="stub"1+17
2
×9+[(class="stub"1
2
-class="stub"1
3
)+(class="stub"1
3
-class="stub"1
4
)+(class="stub"1
4
-class="stub"1
5
)++(class="stub"1
9
-class="stub"1
10
)]

=81+(class="stub"1
2
-class="stub"1
10
),
=81+class="stub"2
5

=81class="stub"2
5

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