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1 supra 1*2 + 1 supra 2*3 + ...+1 supra x(x+1) = 2010 supra 2011

Răspuns :

1/1 - 1/2 + 1/2 - 1/3 +1/3 - 1/4 +.........+1/x - 1/(x+1) = 2010/2011
1/1 - 1/(x+1) = 2010/2011      x/(x+1) = 2010/2011  x= 2010