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27+28+.......+85=,31+32+.....145=,26+27+..........82=,4+45+.......100=

Răspuns :

27+28+...+85=1+2+...+85–(1+2+...+26)=85·86:2–(26·27:2)=3655

31+32+...+145=1+2+...+145–(1+2+…+30)=145·146:2–30·31:2=10585–465=10120

26+27+…+82=82·83:2–25·26:2=3403–325=3078

4+5+...+100=100·101:2–3·4:2=5050–6=5044