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Ajutati-ma, va rog
13/20 < x+1/15 < 11/12


Răspuns :

13/20 < (x+1)/15 < 11/12 , aducem la acelasi numitor (60)
13x3/60<4(x+1)/60<11x5/60
39<4x+4<55, scadem 4
35<4x<51
Pt x apartine lu N=> 35<4x9 si 4x12<51, deci x={9,10,11,12}
Pt x apartine lui R=> x apartine (35/4,51/4)