- #1
latentcorpse
- 1,444
- 0
I just want to check something here.
If we want the radius of convergence of [itex]\sum_{n=0}^{\infty} x^n[/itex], we cannot use the ratio test because its not a series, it's a series of functions i.e. we have [itex]\sum f_n(x)[/itex] not [itex]\sum a_n[/itex]. is this true?
so if we apply the M test to the [itex]f_n[/itex], then we need to find a sequence of positive integers [itex]M_n[/itex] such that [itex]|f_n(x)| \leq M_n \forall x \in E[/itex] where E is our interval.
Then we notice that such an [itex]M_n[/itex] cannot exist for [itex]|x|>1[/itex] and hence for the given power series, teh radius of convergence is [itex]R=1[/itex].
how does this look to everyone?
If we want the radius of convergence of [itex]\sum_{n=0}^{\infty} x^n[/itex], we cannot use the ratio test because its not a series, it's a series of functions i.e. we have [itex]\sum f_n(x)[/itex] not [itex]\sum a_n[/itex]. is this true?
so if we apply the M test to the [itex]f_n[/itex], then we need to find a sequence of positive integers [itex]M_n[/itex] such that [itex]|f_n(x)| \leq M_n \forall x \in E[/itex] where E is our interval.
Then we notice that such an [itex]M_n[/itex] cannot exist for [itex]|x|>1[/itex] and hence for the given power series, teh radius of convergence is [itex]R=1[/itex].
how does this look to everyone?