Does Convergence of Sum(z_j) and Sum((z_j)^2) Imply Convergence of Sum(|z_j|^2)?

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SUMMARY

The discussion centers on the convergence of the series Sum(z_j) and Sum((z_j)^2) in relation to the convergence of Sum(|z_j|^2), where z_j is a complex sequence with a positive real part. It is established that if both Sum(z_j) and Sum((z_j)^2) converge, it does not necessarily imply that Sum(|z_j|^2) converges. The attempt to analyze the real and imaginary components of z_j, specifically breaking it down into x_j and y_j, highlights the complexity of the relationship between these sums.

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Homework Statement


Assume that z_j is a sequence where j indexes from 1 to infinity are in the complex numbers such that the real part of z > 0. Is it true or false that if sum(z_j) and sum_((z_j)^2) both converge then sum(|z^j|^2) also converges?


Homework Equations





The Attempt at a Solution


I tried breaking up z into real and imaginary parts and looking at what has to converge. For example, if z_j=x_j+iy_j, then the sum of x_j and sum of y_j both converge. Not really sure where else to go.
 
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What are the real and imaginary parts of [itex]z_j^2[/itex]?
 
so the real part is x^2-y^2 and the imaginary part is 2xy
 

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