Let $x$ be a small real number, say $1/10
Using the triangle inequality it's easy to find an upper bound for the above sum, but I don't know any method for finding a lower bound.
Would a lower bound like $\vert a_n\vert \geq 2^n$ help?
Let $x$ be a small real number, say $1/10
Using the triangle inequality it's easy to find an upper bound for the above sum, but I don't know any method for finding a lower bound.
Would a lower bound like $\vert a_n\vert \geq 2^n$ help?