Wednesday 11 March 2015

`a_n = nsin(1/n)` Determine the convergence or divergence of the sequence with the given n'th term. If the sequence converges, find its limit.

`a_n=nsin(1/n)`


Apply n'th term test for divergence, which states that, 


If `lim_(n->oo) a_n!=0` , then `sum_(n=1)^ooa_n` diverges


`lim_(n->oo)nsin(1/n)=lim_(n->oo)sin(1/n)/(1/n)`  


Apply L'Hospital's rule,


Test L'Hospital condition:`0/0`


`=lim_(n->oo)(d/(dn)sin(1/n))/(d/(dn)1/n)` 


`=lim_(n->oo)(cos(1/n)(-n^(-2)))/(-n^(-2))`


`=lim_(n->oo)cos(1/n)`


`lim_(n->oo)1/n=0`


`lim_(u->0)cos(u)=1` 


By the limit chain rule,


``


`=1!=0` 


So, by the divergence test criteria series diverges.  


` `

`a_n=nsin(1/n)`


Apply n'th term test for divergence, which states that, 


If `lim_(n->oo) a_n!=0` , then `sum_(n=1)^ooa_n` diverges


`lim_(n->oo)nsin(1/n)=lim_(n->oo)sin(1/n)/(1/n)`  


Apply L'Hospital's rule,


Test L'Hospital condition:`0/0`


`=lim_(n->oo)(d/(dn)sin(1/n))/(d/(dn)1/n)` 


`=lim_(n->oo)(cos(1/n)(-n^(-2)))/(-n^(-2))`


`=lim_(n->oo)cos(1/n)`


`lim_(n->oo)1/n=0`


`lim_(u->0)cos(u)=1` 


By the limit chain rule,


``


`=1!=0` 


So, by the divergence test criteria series diverges.  


` `

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