`#Sad`
`a)`
`32 < 2^n < 128`
`⇔ 2^5 < 2^n < 2^7`
`⇔ 5 < n < 7`
`⇔ n = 6`
`\text{Vậy}` `n=6` `(n in NN^(***))`
`b)`
`2. 16 >= 2^n > 4`
`⇔ 32 >= 2^n > 4`
`⇔ 2^5 >= 2^n > 2^2`
`⇔ 5 >= n > 2`
`⇔ n in {5; 4; 3}`
`\text{Vậy}` `n in {5; 4; 3}` `(n in NN^(***))`
`c)`
`9. 27 <= 3^n <= 243`
`⇔ 243 <= 3^n <= 243`
`⇔ 3^5 <= 3^n <= 3^5`
`⇔ 5 <= n <= 5`
`⇔ n = 5`
`\text{Vậy}` `n=5` `(n in NN^(***))`