Question

  mn giúp em bài 2 2 ý đc ko ạ 

Answer 1

Bài 2:

1: \(\left\{{}\begin{matrix}u_1=1\\u_{n+1}=u_n+3\end{matrix}\right.\)

=>\(u_2=u_1+3=4;u_3=u_2+3=4+3=7\)

\(u_4=u_3+3=7+3=10;u_5=u_4+3=10+3=13\)

=>\(u_n=1+3\left(n-1\right)=1+3n-3=3n-2\)

2: \(\left\{{}\begin{matrix}u_1=3\\u_{n+1}=4u_n\end{matrix}\right.\)

=>\(u_2=4\cdot u_1=4\cdot3=12;u_3=4\cdot u_2=4\cdot12=48\); \(u_4=4\cdot u_3=4\cdot48=192;u_5=4\cdot u_4=4\cdot192=768\)

=>Công thức là \(u_n=3\cdot4^{n-1}\)