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a=(3^21+3^20+3^19):39 Aratati ca a este patratul perfect

Răspuns :

A= 3¹⁹ (3² + 3¹+ 1) :39
A= 3¹⁹ ( 9+3+1) :39
A= 3¹⁸ * 3* 13 :39
A=3¹⁸ * 39:39
A= 3¹⁸ = 3⁹*²= (3⁹)²  - patrat perfect