Đáp án:
Giải thích các bước giải:
a, \(\dfrac{16}{2^n}=2\)
\(2^n=\dfrac{16}{2}\)
\(2^n=8\)
\(2^n=2^3\)
`⇒ n = 3`
b, \(\dfrac{\left(-3\right)^n}{81}=-27\)
\(\left(-3\right)^n=-27\cdot81\)
\(\left(-3\right)^n=\left(-3\right)^3\cdot3^4\)
\(\left(-3\right)^n=\left(-3\right)^7\)
`⇒ n = 7`
c, \(8^n:2^n=4\)
\(2^{3n}:2^n=2^2\)
\(2^{2n}=2^2\)
`⇒ 2n = 2`
`n = 2:2`
`n = 1`
d) `2.16 ≥ 2^n ≥ 4`
`⇒ 32 ≥ 2^n ≥4`
`⇒ 2^5 ≥ 2^n ≥2^2`
`⇒ 5 ≥ n ≥ 2`
`⇒ n ∈ {5;4;3;2}`
e) `9.27 \le 3^n \le -243`
`=>243 \le 3^n \le -243`
`=> n=5`
