Question

2) tìm số tự nhiên n biết:

\(\left(\dfrac{1}{3}\right)^n=\dfrac{1}{27};\left(\dfrac{3}{5}\right)^n=\dfrac{81}{625}\)

Answer 1

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

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

\(\Rightarrow n=3\)

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

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

\(\Rightarrow n=4\)

Answer 2

a, \(\left(\dfrac{1}{3}\right)^n=\dfrac{1}{27}\Rightarrow\left(\dfrac{1}{3}\right)^n=\left(\dfrac{1}{3}\right)^3\)

Vì \(\dfrac{1}{3}\ne-1,\dfrac{1}{3}\ne0;\dfrac{1}{3}\ne1\) nên \(n=3\)

Vậy........

b, \(\left(\dfrac{3}{5}\right)^n=\dfrac{81}{625}\Rightarrow\left(\dfrac{3}{5}\right)^n=\left(\dfrac{3}{5}\right)^4\)

Vì \(\dfrac{3}{5}\ne-1,\dfrac{3}{5}\ne0;\dfrac{3}{5}\ne1\) nên \(n=4\)

Vậy..........

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