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4+7+10+........+2002

Răspuns :

nr de termeni este: (2002-4):3+1=1998:3+1=667  deci  suma va fi:  (2002+4)x667:2=2006x667:2=1003x667=667001
fie S suma data
2S= 4    +7+......+2002+
      2002+2001+...4=
2006+ 2006+ ....+2006=
2006*n, unde n = nr de termeni

2002= 4+(n-1)/3
1998=3(n-1)
n-1=1998:3= 666
n=667

deci 2S= 2006*667
=>S= 2006*667/2= 1003*667

Un An Nou bun!