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a fost răspuns

aflati nr naturalx,astfel incat:11+12+.....100=5(1000x-1)

Răspuns :

11+12+...+100=5(1000x-1)
(1+2+...+100)-(1+2+...+10)=5(1000x-1)

Aplicam:
1+2+...+n=n(n+1)/2

100*101/2 -10*11/2=5(1000x-1)
5050-55=5(1000x-1), impartim la 5

1010-11=1000x-1
1000x=1000

x=1

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