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a=2005+2*(1+2+3+...+2004) este patrat perfect

Răspuns :

1+2+3+....+2004=2005x2004:2=2005x1002

A=2005+2005x2004=2005x2005=2005 la patrat deci e patrat perfect
1+2+3......+2004=2005×2004÷2=2005×1002 A=2005 +2005×2004=2005×2005=2005^ deci este pp