Question

Answer 1

2)

a) Ta có: \(VT=\dfrac{\left(5^4-5^3\right)^3}{125^5}=\dfrac{\left(5^3.5-5^3\right)^3}{\left(5^3\right)^5}=\dfrac{\left[5^3\left(5-1\right)\right]^3}{\left(5^3\right)^5}=\dfrac{\left(5^3\right)^3.4^3}{\left(5^3\right)^5}=\dfrac{4^3}{\left(5^3\right)^2}=\dfrac{4^3}{\left(5^2\right)^3}=\dfrac{64}{25^3}=VP\) (đpcm)

3) \(9\le3^n< 1000\)

\(9\le3^n< 729\)

\(3^2\le3^n< 3^6\)

\(\Rightarrow n\in\left\{2;3;4;5\right\}\)