2•(1+2+3+....+2004)+2005 este pătrat perfect

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Grade: Education Subject: matematica
2•(1+2+3+....+2004)+2005 este pătrat perfect
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2•(1+2+3+....+2004)+2005= 2* 2004*2005/2+2005 = 2004*2005+2005=
=2005*( 2004+1)= 2005*2005= 2005²


Pt.
1+2+3+....+2004 aplici  S= n*(n+1) /2