计算:15×7+17×9+19×11+111×13+…+1个3×个5=______.-数学

题目简介

计算:15×7+17×9+19×11+111×13+…+1个3×个5=______.-数学

题目详情

计算:
1
5×7
+
1
7×9
+
1
9×11
+
1
11×13
+…+
1
个3×个5
=______.
题型:填空题难度:中档来源:不详

答案

class="stub"t
5×7
+class="stub"t
7×9
+class="stub"t
9×tt
+class="stub"t
tt×te
+…+class="stub"t
2e×25

=class="stub"t
2
×
class="stub"t
5
-class="stub"t
7
+class="stub"t
7
-class="stub"t
9
+class="stub"t
9
-class="stub"t
tt
+class="stub"t
tt
-class="stub"t
te
+…+class="stub"t
2e
-class="stub"t
25
),
=class="stub"t
2
×(class="stub"t
5
-class="stub"t
25
),
=class="stub"t
2
×class="stub"1
25

=class="stub"2
25

故答案为:class="stub"2
25

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