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se consdidera numarul a=8supra7 - 15supra21 + 72supra56 + 2supra7
aratati ca aeN


Răspuns :

a= 8/7-15/21+72/56+2/7=8/7-5/7+72/56+2/7=8/7-5/7+9/7+2/7=8-5+9+2/7=19-5/7=14/7=2 care apartine N (multimea nr naturale)