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calculeaza 11+12+..... 99 suma gauss

Răspuns :

11 + 12 +...+ 99 =

= (1+2+3+...+99) - (1+2+3+...+10) =

= 99 × (99+1) : 2 - 10×(10+1) : 2 =

= 99 × 100 : 2 - 10×11:2 =

= 99 × 50 - 5 × 11 =

= 4 950 - 55 =

= 4 895