Extract Real Part From ln(e^{ix}+i)

  • Thread starter cragar
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In summary, the conversation discusses taking the real part of ln(e^{ix}+i) and finding an alternate way to integrate sec(x) using Euler's formula. One method involves using the complex logarithm and the other involves using the complex module and argument.
  • #1
cragar
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How do I take the real part of this
[itex] ln(e^{ix}+i) [/itex]
I know you can write the arctan(x) in terms of logs with complex numbers should I do something like that? I came across this because I was trying to integrate sec(x) with Eulers formula.
 
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  • #2
cragar said:
How do I take the real part of this
[itex] ln(e^{ix}+i) [/itex]
I know you can write the arctan(x) in terms of logs with complex numbers should I do something like that? I came across this because I was trying to integrate sec(x) with Eulers formula.



$$e^{ix}+i=\cos x+i\sin x+i=\cos x+(\sin x+1)i\Longrightarrow Log(e^{ix}+i)=\frac{1}{2}\log\left(\cos^2x+(\sin x+1)^2\right)+i\arg(e^{ix}+i)$$

So never mind what branch of the complex logarithm we choose, the real part is:

$$\frac{1}{2}\log\left(\cos^2x+(\sin x+1)^2\right)=\frac{1}{2}\log\left(2(1+\sin x)\right)$$
 
  • #3
where did you get the cos(x)^2 and what does arg mean
 
  • #4
Another way :
2*Real part = ln(exp(ix)+i)+ln(exp(-ix)-i)
(exp(ix)+i)*(exp(-ix)-i) = 1-i*exp(ix)+i*exp(-ix)+1 = 2+2sin(x)
Real part =(1/2) ln(2+2sin(x))
 
  • #5
cragar said:
where did you get the cos(x)^2 and what does arg mean

Cosine square is part of the (complex) module (or absolute value) of the complex number written there, and arg = argument.

DonAntonio
 

1. What is the purpose of extracting the real part from ln(e^{ix}+i)?

The purpose of extracting the real part from ln(e^{ix}+i) is to simplify the expression and make it easier to solve or manipulate in mathematical equations. By isolating the real part, it becomes easier to analyze and understand the behavior of the equation.

2. How do you extract the real part from ln(e^{ix}+i)?

To extract the real part from ln(e^{ix}+i), we can use the properties of logarithms and Euler's formula. First, we can rewrite ln(e^{ix}+i) as ln(e^{ix}*(1+i)). Then, we can use the property ln(ab) = ln(a) + ln(b) to split the expression into ln(e^{ix}) + ln(1+i). Finally, we can use Euler's formula, e^{ix} = cos(x) + i*sin(x), to simplify ln(e^{ix}) to ix. Therefore, the real part of ln(e^{ix}+i) is just the imaginary part of ix, which is x.

3. Is extracting the real part from ln(e^{ix}+i) always necessary?

No, extracting the real part from ln(e^{ix}+i) is not always necessary. It depends on the specific problem or equation you are trying to solve. Sometimes, it may be more useful to keep the expression in its original form or extract the imaginary part instead.

4. What is the real part of ln(e^{ix}+i) if x = 0?

If x = 0, the real part of ln(e^{ix}+i) would be 0. This is because when x = 0, ln(e^{ix}+i) becomes ln(1+i), which can be simplified to ln(sqrt(2)) = 0.

5. Can the real part of ln(e^{ix}+i) be negative?

Yes, the real part of ln(e^{ix}+i) can be negative. It depends on the value of x. For example, if x = -pi/2, the real part would be -pi/2. However, in most cases, the real part would be positive or 0.

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