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Oriancristian
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calculati sumele 3+6+9+12+.........+3000

Răspuns :

Icecon2005
3(1+2+3+4+....+1000)
suma gauss S=n(n+1)]:2
S=3×1000*1001:2=1501500

S=1501500
2)
3+6+9+12+.........+3000 -este progresie aritmetica, r-ratia, =3, cresc nr din 3 in 3
an=a1+(n-1)*r
3+6+9+12+.........+3000
3000=3+(n-1)*3
3000=3+3n-3
n=1000
S=[(an+a1)*n]:2
S=[(3000+3)*1000]:2
S=(3003*1000):2
S=1501500

Ramona19852007
3 + 6 + 9 +12 + ..........+3000  =
n = ( 3000 - 3 ) : ( 6 - 3 ) +1 =
n = 2997 : 3 + 1=
n = 999 +1
n = 1000

S = [( 3000 + 3 ) x 1000 } : 2 
S = (3003 x 1000 ) : 2 
S = 3003000 : 2
S = 1501500.

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