Răspuns:
x ∈ {91 , 92 , 93 , 94 , 95 , 96 , 97 , 98 , 99}
Explicație pas cu pas:
1/10 < 10/x <1/9 ; x ∈ N* ; x = ?
⁹⁾1/10 < ⁹⁰⁾10/x <¹⁰⁾1/9 <=>
ˣ⁾9/90 < 900/90x < ˣ⁾10/90 <=>
9x < 900 < 10x
9x < 900 I :9 => x < 100
900 < 10x I :10 => 90 < x
=> x ∈ (90 , 100) I x ∈ N* =>
x ∈ {91 , 92 , 93 , 94 , 95 , 96 , 97 , 98 , 99}
