Question #348464

Find, showing all working, a recursive de nition of the sequence with general

term

tn = 3 (n + 1)!/2n ; n >= 1


1
Expert's answer
2022-06-06T23:23:42-0400

tn=3(n+1)!2n;n1t_n =\frac{ 3 (n + 1)!}{2n} ; n \geq1; will be the general term of the sequence.


Let's find the next term:

tn+1=3((n+1)+1)!2(n+1)=3(n+2)!2(n+1)=t_{n +1}=\frac{ 3 ((n + 1)+1)!}{2(n+1)}=\frac{ 3 (n+2)!}{2(n+1)}=


=3(n+2)(n+1)n×...×12(n+1)=3(n+2)(n+1)!2(n+1)nn==\frac{ 3 (n+2)(n+1)n\times...\times1}{2(n+1)}=\frac{ 3 (n+2)(n+1)!}{2(n+1)}\frac{n}{n}=


=3(n+1)!2nn(n+2)n+1=tnn(n+2)n+1=n(n+2)n+1tn.=\frac{ 3 (n+1)!}{2n}\frac{n(n+2)}{n+1}=t_n\frac{n(n+2)}{n+1}=\frac{n(n+2)}{n+1}t_n.


Also we have to find the first term:

t1=3(1+1)!21=32!2=322=3.t_1 =\frac{ 3 (1 + 1)!}{2\cdot 1}=\frac{3\cdot 2!}{2}=\frac{3\cdot 2}{2}=3.


So, the recursive de finition of the sequence is as follows:

t1=3,t_1=3,

tn+1=n(n+2)n+1tn.t_{n+1}=\frac{n(n+2)}{n+1}t_n.


Answer:

t1=3,t_1=3,

tn+1=n(n+2)n+1tn.t_{n+1}=\frac{n(n+2)}{n+1}t_n.



But if we have 2n2^n in denominator, the solution is the next:

tn=3(n+1)!2n;n1t_n =\frac{ 3 (n + 1)!}{2^n} ; n \geq 1; will be the general term of the sequence.

Let's find the next term:

tn+1=3((n+1)+1)!2n+1=3(n+2)!2n+1=t_{n +1}=\frac{ 3 ((n + 1)+1)!}{2^{n+1}}=\frac{ 3 (n+2)!}{2^{n+1}}=


=3(n+2)(n+1)n×...×12n21=3(n+1)!2nn+22=tnn+22.=\frac{ 3 (n+2)(n+1)n\times...\times1}{2^n\cdot 2^1}=\frac{ 3(n+1)!}{2^n}\frac{n+2}{2}=t_n\frac{n+2}{2}.


Also we have to find the first term:

t1=3(1+1)!21=32!2=322=3.t_1 =\frac{ 3 (1 + 1)!}{2^1}=\frac{3\cdot 2!}{2}=\frac{3\cdot 2}{2}=3.


So, the recursive defi nition of the sequence is as follows:

t1=3,t_1=3,

tn+1=n+22tn.t_{n+1}=\frac{n+2}{2}t_n.


Answer:

t1=3,t_1=3,

tn+1=n+22tn.t_{n+1}=\frac{n+2}{2}t_n.


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