Question

Tìm số tự nhiên n biết:

a) (1​​​​/3)^​n​=1/27

​b)(3/5)^​n​=81/625

​c)3ⁿ.2ⁿ​=36

​d)2^​n/3ⁿ=8/27

Answer 1

a) \(\left(\frac{1}{3}\right)^n=\frac{1}{27}\)

\(\left(\frac{1}{3}\right)^n=\left(\frac{1}{3}\right)^3\)

\(\Rightarrow n=3\)

b) \(\left(\frac{3}{5}\right)^n=\frac{81}{625}\)

\(\left(\frac{3}{5}\right)^n=\left(\frac{3}{5}\right)^4\)

\(\Rightarrow n=4\)

c) \(3^n\cdot2^n=36\)

\(\left(3\cdot2\right)^n=36\)

\(6^n=6^2\)

\(\Rightarrow n=2\)

d) \(\frac{2^n}{3^n}=\frac{8}{27}\)

\(\left(\frac{2}{3}\right)^n=\left(\frac{2}{3}\right)^3\)

\(\Rightarrow n=3\)