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aratati ca numarul A=2021 +2•(1+2+3+.......+2020)este patrat perfect.

Răspuns :

a=2021+2x(2020x2021:2)
=2021+2020x2021
=2021x(1+2020)
=2021x2021
=2021²
A=2021+2*(2020*2021)/2=2021+2020*2021=2021(1+2020)=2021*2021=2021 la puterea 2=> A este patrat perfect