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Calculati sirul : 22+24+26+...+262+264=?
Ajutati-ma, va roooog!


Răspuns :

2(11+12+...+132)-2(1+2+...10) =
2x132*133:2 - 2x10x11":2 =
17556 - 110 = 
= 17446
22+24+26+...+262+264=
= 2(11+12+13+...+131+132) =
= 2[(1+2+3+...+132) - (1+2+...+10)]=
= 2(132×133:2 - 10×11:2) =
= 132×133 - 10×11 =
= 17 556 - 110 =
= 17 446
la rezolvarea acestui exercitiu am folosit suma lui Gauss.