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Question : 137 of 180
Marks:
+1,
-0
Solution:
We have,
113+‌123+133+...+203=(13+23+...+103+113+.‌123+....+203)‌−(13+23+....+103) ‌=Σ(20)3−Σ(10)3‌=(‌)2−(‌)2‌=(10×21)2−(5×11)2=(210−55)(210+55)‌=155×265=41075=5×8215
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