a: \(\Leftrightarrow2< x< =5\)

hay \(x\in\left\{3;4;5\right\}\)

2.16 ≥ 2n > 4 ⇒ 2. 24 ≥ 2n > 22

⇒ 25 ≥ 2n > 22

⇒ 5 ≥ n > 2

⇒ n ∈ {3; 4; 5}

Đáp án B

a).

\(2.16=2.2^4=2^5\\ 4=2^2\)

theo đề bài, ta có: \(2^5\ge2^n>2^2\Rightarrow5\ge n>2\)

vì n là số tự nhiên nên : \(n=5;4;3\)

b).

\(9.27=3^2.3^3=3^5\\ 243=3^5\)

theo đề bài, ta có: \(3^5\le3^n\le3^5\Rightarrow5\le n\le5\)

=> n=5

Giải:

a)2.16\(\ge\)2ⁿ>4

2.2⁴\(\ge\)2ⁿ>2²

2⁵\(\ge\)2ⁿ>2²

\(\Rightarrow\)5\(\ge\)n>2

\(\Rightarrow\)n\(\in\){3;4;5}

b)9.27\(\le\)3ⁿ\(\le\)243

3².3³\(\le\)3ⁿ\(\le\)3⁵

3⁵\(\le\)3ⁿ\(\le\)3⁵

5\(\le\)n\(\le\)5

\(\Rightarrow\)n=5

a) 2.16\(\ge\)2ⁿ>4

=>2.2⁴\(\ge\)2ⁿ>4

=>2^5\(\ge\)2ⁿ>2²

^{=>5\(\ge\)n>2}

^=>n\(\in\){3,4,5}

b)9.27\(\le\)3ⁿ\(\le\)243

=>3².3³\(\le\)3ⁿ\(\le\)3⁵

=>3⁵\(\le\)3ⁿ\(\le\)3⁵

=>5^\(\le\)n\(\le\)5

=>n=5

a. 2.16 \(\ge\)2ⁿ>4

=> 32 \(\ge\)2ⁿ>4

=> 2⁵ \(\ge\)2ⁿ>2²

=> n \(\in\left\{3;4;5\right\}\)

b. \(9.27\le3^n\le243\)

=> \(243\le3^n\le243\)

=> \(3^5\le3^n\le3^5\)

=> n=5

a, \(2.16\ge2^n>4\Rightarrow2^5\ge2^n>2^2\Rightarrow5\ge n>2\Rightarrow n\in\left\{3;4;5\right\}\)

b,\(9.27\le3^n\le243\Rightarrow3^5\le3^n\le3^5\Rightarrow n=5\)

9.27 ≤ 3n ≤ 243 ⇒ 32.33 ≤ 3n ≤ 35

⇒ 35 ≤ 3n ≤ 35 ⇒ n = 5

a) 2.16>2ⁿ>4 (6==>4)

2.2⁴>2ⁿ>2²

2⁵>2ⁿ>2²

==> 5>n>2

n€{5;4;3}

b) 9.27<3ⁿ<243

3².3³<3ⁿ<3⁵

3⁵<3ⁿ<3⁵

==> 5<n<5

==> n=5

Đề sai rồi nha bạn phải là tìm n(n€N)