How Can You Simplify the Inequality |Im(z^2 - z̅ + 6)| < 12 Given |z| < 3?

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SUMMARY

The discussion focuses on simplifying the inequality |Im(z² - z̅ + 6)| < 12 under the condition |z| < 3, where z is a complex number represented as z = x + iy. The key transformation involves calculating |Im(z² - z̅ + 6)|, which simplifies to |2xy + y|. The participant successfully proved the inequality using Lagrange multipliers but seeks a more straightforward arithmetic approach, suggesting the use of the triangle inequality and properties of complex numbers.

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  • Familiarity with complex conjugates and their properties.
  • Knowledge of the triangle inequality in complex analysis.
  • Experience with optimization techniques, including Lagrange multipliers.
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Homework Statement



Know: modulus(z) < 3
WTS: |Im(z2 - zbar + 6)| <12

where zbar is the complex conjugate

Homework Equations



z = x + iy

The Attempt at a Solution



|Im(z2 - zbar + 6)|
= |Im(x2 + 2i*x*y - y2 - x + iy + 6)|
= |2xy + y|

So I want to show |2xy + y|< 12

I already proved it using maximization and Lagrange multipliers, but it seems like overkill, and I think there is some kind of arithmetic trick I am missing. Anyone see it?

Thanks
 
Last edited:
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|Im(z)|[tex]\leq[/tex] |z|
Then use the triangle inequality to derive an upper bound.
 
One thing to be careful about is to use:
[tex] |z_{1}-z_{2}|\leqslant ||z_{1}|-|z_{2}||[/tex]
 

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