13+115…+199=-数学

题目简介

13+115…+199=-数学

题目详情

1
3
+
1
15
…+
1
99
=
题型:解答题难度:中档来源:不详

答案

class="stub"1
3
+class="stub"1
15
+…+class="stub"1
99

=class="stub"1
3
+class="stub"1
3×5
+…+class="stub"1
9×11

=class="stub"1
2
×(1-class="stub"1
3
+class="stub"1
3
-class="stub"1
5
+…+class="stub"1
9
-class="stub"1
11
),
=class="stub"1
2
×(1-class="stub"1
11

=class="stub"1
2
×class="stub"10
11

=class="stub"5
11

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