S = 2+ 4+ 6.....+996+998+1000
S = 1000+998+996.....+ 6+ 4+ 2
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2 S = 1002+1002+1002+.........+1002+1002+1002
Stabilim cati termeni are suma
2, 2+2*1, 2+3*1.............2+2*499
suma are 500 de termeni
2S = 1002*500
2S = 501000
s = 501000: 2
S = 250500
la fel se rezolva si celelalte
sper sa fie bine