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Determinati valoarea sumei 23 +24+25+...+85
Va rog,urgent!!!!


Răspuns :

Suma lui Gauss: 1+2+3+...+n=[n(n+1)]/2
Lipsește 1+2+3+...+22 din sumă.
S=23+24+25+...+85-(1+2+3+...+22)
S=(85*86)/2-(22*23)/2
S=85*43-11*23
S=3655-253
S=3402
1+2+3+...+22=22•23/2=253
1+2+3+...+23+24+25+...+85=85•86/2=85•43
=3655
3655-253=3402