t**********g
发帖数: 30 | 1 To prove the h[n]=(sin0.4n)/n is not abosolutely summable.
That means sum(h[n]) (n=1->infinity ) is infinity |
b****d
发帖数: 1311 | 2
max{ |sin 0.4n|, |sin 0.4(n+1)| } >= sin 0.2
【在 t**********g 的大作中提到】
: To prove the h[n]=(sin0.4n)/n is not abosolutely summable.
: That means sum(h[n]) (n=1->infinity ) is infinity
|
t**********g
发帖数: 30 | 3 ? I do not uderstand. even so
how to prove sum(|sin 0.4n|/n) n=1,2,..,infinite. is infinity?
【在 b****d 的大作中提到】
:
: max{ |sin 0.4n|, |sin 0.4(n+1)| } >= sin 0.2
|
b****d
发帖数: 1311 | 4 show that at least one of |sin0.4n|, |sin0.4(n+1)|,
is greater than some number t.
【在 t**********g 的大作中提到】
: To prove the h[n]=(sin0.4n)/n is not abosolutely summable.
: That means sum(h[n]) (n=1->infinity ) is infinity
|
t**********g
发帖数: 30 | 5 yes I also want to find a minium.
But it seems that when n->infinity min(sin(0.4n))->0
It can not work
【在 b****d 的大作中提到】
: show that at least one of |sin0.4n|, |sin0.4(n+1)|,
: is greater than some number t.
|
x******g
发帖数: 318 | 6 记|sin0.4n|/n=f(n)
则f(1)+f(2)>sin0.2/2
f(3)+f(4)>sin0.2/4
...
所以f(1)+...f(2n)>sin0.2(1/2+...+1/2n)趋于无穷
【在 t**********g 的大作中提到】
: ? I do not uderstand. even so
: how to prove sum(|sin 0.4n|/n) n=1,2,..,infinite. is infinity?
|
w**z
发帖数: 45 | 7 nice
【在 x******g 的大作中提到】
: 记|sin0.4n|/n=f(n)
: 则f(1)+f(2)>sin0.2/2
: f(3)+f(4)>sin0.2/4
: ...
: 所以f(1)+...f(2n)>sin0.2(1/2+...+1/2n)趋于无穷
|
