a^2 = 2016^2 - 2016 - 2015
a^2 = 2016 × 2016 - 2016 - 2015
dăm factor comun pe 2016
a^2 = 2016 × (2016 - 1) - 2015
a^2 = 2016 × 2015 - 2015
dăm factor comun pe 2015
a^2 = 2015 × (2016 - 1)
a^2 = 2015 × 2015
a × a = 2015 × 2015
==> a = 2015
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^ = simbol folosit ptr ridicarea la putere