What Is the Argument of j to the Fourth Power?

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Discussion Overview

The discussion centers around determining the argument of the complex number \( j^4 \), where \( j \) represents the imaginary unit. Participants explore the relationship between the argument of \( j \) and its powers, particularly in polar form, and how these relate to the properties of complex numbers.

Discussion Character

  • Exploratory
  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • One participant suggests that the argument of \( j \) is \( \frac{\pi}{2} \) and proposes a method for calculating the argument of \( j^2 \) and \( j^4 \).
  • Another participant challenges this by asking for the equivalent of \( j^4 \) and introduces the formula for the argument of a complex number.
  • A request for clarification in polar form is made, indicating that \( z = 1(\cos(\frac{\pi}{2}) + j\sin(\frac{\pi}{2})) \) represents the argument of \( j \).
  • One participant explains that the argument is simply \( \theta \) in polar form and provides a table of values for powers of \( j \).
  • Another participant notes that since \( j^4 = 1 \), the imaginary part of \( z \) is zero and questions what value of \( \theta \) results in \( \sin(\theta) \to 0 \).
  • Responses indicate that \( \sin(0) = 0 \) and request a final answer regarding the argument.
  • One participant concludes that \( \text{arg}(j^4) = 0 \) because \( j^4 \) lies on the positive real axis.
  • Another participant asserts that while \( j^4 = 1 \), the argument is indeed zero, reinforcing the relationship between the argument and the position on the complex plane.
  • Further clarification is provided that positive values on the real axis have an argument of 0, while positive imaginary values have an argument of \( \frac{\pi}{2} \).
  • One participant expresses gratitude for the assistance provided in the discussion.

Areas of Agreement / Disagreement

Participants generally agree that \( j^4 = 1 \) and that the argument of \( j^4 \) is zero. However, there is some confusion regarding the calculation of arguments for powers of \( j \), with differing interpretations of how to derive these values.

Contextual Notes

Some participants express uncertainty about the calculations and relationships between the arguments of different powers of \( j \), particularly regarding the multiplication of arguments and the implications of squaring complex numbers.

aliz_khanz
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okie ... one attempt as i see it ...

argument of j is pie/2 ... so argument of j^2 will be pie square/ 4 and so on ...

is it right?
 
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No. Here's a hint: what is j4 equivalent to?

For some number z=x+y\mathrm{j} \in \mathbb{C}, \mathrm{arg}(z) \equiv \arctan(\frac{y}{x}).
 
Dear Jhae2.718 ... can you please explain it in polar form?

for example...

z= 1(cos pie/2 +jsinpie/2) is the argument of j ...i don't know what to do for j^4
 
For polar form, the argument is just \theta.

Keep in mind that we're using z = r\cos(\theta)+\mathrm{j}r\sin(\theta).

For jn, you'll want to simplify a bit. Recall:
Code:
n      j[sup]n[/sup] 
-----------------------
1      j
2     j*j = - 1
3     j*j[sup]2[/sup] = -j
4     j*j[sup]3[/sup] = 1
.
.
.
 
so i take from your explanation that ...

z= rcos (theta) + rsin (theta) *since j^4=1
 
j4 =1, which means that the imaginary part of z is zero. What value of \theta makes \sin(\theta) \to 0?
 
sin 0 = 0

can you please provide me the final answer of this bro? :)
 
arg(j^4) = 0, since j^4 is on the positive real axis and the argument is the angle between the complex no. and the positive real axis.
 
shouldnt it be 1? because sin theta goes to zero , but cos theta goes to 1 !
 
  • #10
j^4 is 1, but the argument of j^4 is zero. As a general rule, positive values on the real axis have an arg of 0 and positive imaginary values have an arg of pi/2.

Remember, in polar coordinates the argument is just the angle theta!
 
  • #11
Thankyou so so so so so so times infinity much ! Really ... ! May God Bless You with A billion dollar or equivalent ! :)
 
  • #12
No problem :wink:

If you want to read more about complex arguments, you can look at the http://en.wikipedia.org/wiki/Argument_(complex_analysis)" . It gets a bit technical, but the graphs should help.
 
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  • #13
aliz_khanz said:
okie ... one attempt as i see it ...

argument of j is pie/2 ... so argument of j^2 will be pie square/ 4 and so on ...

is it right?
No, squaring a number multiplies the argument by 2- it does not square it! The argument of j^4 is 4(\pi/2)= 2\pi (or 0 since adding or subtracting any multiple of 2pi won't change the answer.)

Of, same same thing, j^2= -1 so j^4= (j^2)(j^2)= (-1)(-1)= 1 which has argument 0.
 

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