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5+6+7+...+103+104=?Va rog,ajutati-ma!!!

Răspuns :

S=[ (A1 +An ) . n] :2 = [( 5+104).104]:2 = (109.104):2=11336:2=5668
s=[(5+104)xnr. termeni]:2
nr.termeni=(104-5):1+1
=99:1+1
100
s=[(5+104)x100]:2
s=(109x100):2
s=10900:2
s=5450