let D be the region in the xy plane in which the series
Summation (x+2y)^k / k converges.
then the interior of D is
A) an open disk
B) the open region bounded by an ellipse
C) the open region bounded by a quadrilateral
D) the open region bounded by 2 parallel lines
E) an open half plane
GR9768 Q 51
Re: GR9768 Q 51
speedychaos4 wrote:is it D?
Yes, can you explain ? Thanks

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Re: GR9768 Q 51
Use the ratio test, you can get r=x+2y, in order to ensure convergence, you want r<1, and therefore you have the ans.
Re: GR9768 Q 51
Great.speedychaos4 wrote:Use the ratio test, you can get r=x+2y, in order to ensure convergence, you want r<1, and therefore you have the ans.
Thanks Speedy