MHB Struggling with Complex Number Function? Need Help?

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The discussion focuses on solving two complex number problems involving factorization and limits. The first question involves factorizing the expression \(4z^2 + 1\) and evaluating the limit as \(z\) approaches \(\frac{1}{2} i\) using the function definition. Participants emphasize the importance of proper substitution and simplification to find the correct limit, which is determined to be \(2i\). The second question addresses finding values \(a\) and \(b\) that ensure continuity at \(z = \frac{1}{2} i\), with suggestions that \(a + bi\) should match the limit value from the first question. The conversation highlights the need for careful evaluation and correction of mistakes in the calculations.
jaychay
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lim 1.png
lim 2.png


Can you help me with this two questions
I am really struggle on how to do it
Please help me

Thank you in advance
 
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Factorize $(4z^2 + 1) = (4z^2 - i^2)= (2z+i)(2z-i)$
 
DaalChawal said:
Factorize $(4z^2 + 1) = (4z^2 - i^2)= (2z+i)(2z-i)$
How can I solve the limit
 
jaychay said:
How can I solve the limit
Substitute the hint DaalChawal gave into the function definition of $f(z)$ and simplify it.
Then substitute the limit point $z=\frac 12 i$ for $f(z)$ with $z\ne \frac 12 i$ and evaluate it.
How far do you get?
 
Last edited:
Klaas van Aarsen said:
Substitute the hint DaalChawal gave into the function definition of $f(z)$ and simplify it.
Then substitute the limit value $z=\frac 12 i$ for $f(z)$ with $z\ne \frac 12 i$ and evaluate it.
How far do you get?
On question 2
Can you tell me on how to find (a,b) that can make it continue at z=1/2i
 
jaychay said:
On question 2
Can you tell me on how to find (a,b) that can make it continue at z=1/2i
Choose $a$ and $b$ such that $a+bi$ is the same as the limit value from question 1.
Did you find the limit value or are you stuck somewhere?
 
Klaas van Aarsen said:
Choose $a$ and $b$ such that $a+bi$ is the same as the limit value from question 1.
Did you find the limit value or are you stuck somewhere?
[/QUOT
Did I do it correct ?
 

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You made a mistake there bro
$2(\frac{i}{2})+i = 2i$
 
jaychay said:
Did I do it correct ?
The first substitution is correct, but the parentheses are placed the wrong way in the substitution of $z=\frac 12 i$.
It should be:
$$\lim_{z\to\frac 12i} f(z) = \lim_{z\to\frac 12i} \frac{4z^2+1}{2z-i} = \ldots = \lim_{z\to\frac 12i} 2z+i = 2\left(\frac 12 i\right) +i=2i$$
 
  • #10
Tha
DaalChawal said:
You made a mistake there bro
$2(\frac{i}{2})+i = 2i$
Thank you bro
 
  • #11
Klaas van Aarsen said:
Substitute the hint DaalChawal gave into the function definition of $f(z)$ and simplify it.
Then substitute the limit point $z=\frac 12 i$ for $f(z)$ with $z\ne \frac 12 i$ and evaluate it.
How far do you get?
Can you please check me on my another post on complex graph equation problem on question 2 on how to find ( a, b )
 
  • #12
Klaas van Aarsen said:
The first substitution is correct, but the parentheses are placed the wrong way in the substitution of $z=\frac 12 i$.
It should be:
$$\lim_{z\to\frac 12i} f(z) = \lim_{z\to\frac 12i} \frac{4z^2+1}{2z-i} = \ldots = \lim_{z\to\frac 12i} 2z+i = 2\left(\frac 12 i\right) +i=2i$$
On question 2
Is ( a,b ) equal to ( 0,2 ) right ?
 
  • #13
Klaas van Aarsen said:
The first substitution is correct, but the parentheses are placed the wrong way in the substitution of $z=\frac 12 i$.
It should be:
$$\lim_{z\to\frac 12i} f(z) = \lim_{z\to\frac 12i} \frac{4z^2+1}{2z-i} = \ldots = \lim_{z\to\frac 12i} 2z+i = 2\left(\frac 12 i\right) +i=2i$$
Klaas van Aarsen said:
Substitute the hint DaalChawal gave into the function definition of $f(z)$ and simplify it.
Then substitute the limit point $z=\frac 12 i$ for $f(z)$ with $z\ne \frac 12 i$ and evaluate it.
How far do you get?
On question 2
Is ( a,b ) equal to ( 0,2 ) right ?
 

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