Question

Answer 1

\(u_n=u_1\cdot q^{n-1}\)

\(\Rightarrow48=3\cdot2^{n-1}\Rightarrow2^{n-1}=16=2^4\)

\(\Rightarrow n-1=4\Rightarrow n=5\)

Chọn B

Answer 2

\(ADCT:u_n=u_1.q^{n-1}\left(n\ge2\right)\\ \Leftrightarrow48=3.2^{n-1}\\\Leftrightarrow 2^{n-1}=16=2^4\\ \Leftrightarrow n-1=4\\ \Leftrightarrow n=5\\ \Rightarrow B\)