Question

Tìm số tự nhiên n, biết :

a) 

b) 

c) 

 

Answer 1

\(\frac{16}{2^n}=2\)

=> 2ⁿ=16:2

=> 2ⁿ=8

=> 2ⁿ=2³

=> n=3

b;

\(\frac{\left(-3\right)^n}{81}=-27\)

\(\Rightarrow\left(-3\right)^n=-27.81\)

=> (-3)ⁿ=-2187

=> (-3)ⁿ=(-3)⁷

=> n=7

c ; \(8^n:2^n=4\)

\(\Rightarrow\left(8:2\right)^n=4\)

\(\Rightarrow\left(4\right)^n=4\)

Mà : 4=4¹

=> 4ⁿ=4¹

=> n=1

Answer 2

\(\frac{16}{2^n}=2\)

\(16:2^n=2\)

\(2^4:2^n=2\)

\(2^n=2^4:2\)

\(2^n=2^3\)

\(=>n=3\)

\(\frac{\left(-3\right)^n}{81}=-27\)

\(\left(-3\right)^n:81=-27\)

\(\left(-3\right)^n=-27\cdot81\)

\(\left(-3\right)^n=-2187\)

\(\left(-3\right)^n=\left(-3\right)^7\)

\(=>n=7\)

 

Answer 3

a) 16/2ⁿ=2 => 2ⁿ=16 : 2=8=2³ => n=3

b) (-3)ⁿ/81= -27 =>(-3)ⁿ= -27 * 81= -2187 =(-3)⁷=> n=7

c) 8n : 2ⁿ = 4 => (8 : 2)ⁿ= 4=> 4ⁿ= 4 => n=1