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

This is because the absolute value of a complex number is not the same as its magnitude. In summary, the problem is to prove |2xy + y|< 12 by using the fact that |z|< 3 for a complex number z and the triangle inequality for complex numbers.
  • #1
jav
35
0

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:
Physics news on Phys.org
  • #2
|Im(z)|[tex]\leq[/tex] |z|
Then use the triangle inequality to derive an upper bound.
 
  • #3
One thing to be careful about is to use:
[tex]
|z_{1}-z_{2}|\leqslant ||z_{1}|-|z_{2}||
[/tex]
 

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

What are complex numbers?

Complex numbers are numbers that contain a real part and an imaginary part. They are typically written in the form a + bi, where a is the real part and bi is the imaginary part, with i representing the square root of -1.

How do you add and subtract complex numbers?

To add or subtract complex numbers, simply add or subtract the real parts and the imaginary parts separately. For example, (2+3i) + (5+2i) = (2+5) + (3+2)i = 7+5i.

What is the conjugate of a complex number?

The conjugate of a complex number is the number with the same real part but the opposite sign on the imaginary part. For example, the conjugate of 2+3i is 2-3i.

How do you multiply complex numbers?

To multiply complex numbers, use the FOIL method (First, Outer, Inner, Last). For example, (2+3i)(5+2i) = 10 + 4i + 15i + 6i^2 = 10 + 19i - 6 = 4 + 19i.

How do you divide complex numbers?

To divide complex numbers, multiply both the numerator and denominator by the conjugate of the denominator. This will result in a real number in the denominator, making it easier to divide. For example, (2+3i) / (5+2i) = (2+3i)(5-2i) / (5+2i)(5-2i) = (10+4i-15i-6i^2) / (25-4i^2) = (16-11i) / 29.

Back
Top