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Aratati ca A=2021+2×(1+2+3+...+2020) este patrat perfect. Va rog raspundetimi!:(

Răspuns :

1+2+3+4+5+6+......+2020=(2020*2021):2
2021+2*(2020*2021):2=2021+2020+2021=2021(2020+1)=2021*2021=patrat perfect
A=2021+2×(1+2+3+...+2020)=2021+2x(2020x2021:2)=2021+(2020x2021=2021(1+2020)=2021x2021=2021²  deci este patrat perfect