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Calcuati
1+2+3+.......+20=


Răspuns :


1+2+3+.....+20=21x20:2=21x10=210

Suma Gaus

n x (n+1 ) : 2

Gauss zice asa
1+2+3+...+n = n(n+1)/2

Noi avem
1+2+3+...+20
Adica n=20
Aplicand formula avem:
20*(20+1)/2 = 
20*21/2 = 
Simplificam 20 cu 2=
10*21 = 210