A little help with this complex number question

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    Complex Complex number
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Discussion Overview

The discussion revolves around a complex number problem involving the expression for a complex number z in terms of polar coordinates. Participants are trying to determine the absolute value of z, denoted as |z|, and are exploring the implications of the coefficients in the expression.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant presents the expression for z as z = 2r cos(x) + r i sin(x) and seeks to find |z|, expressing frustration over the lack of a single numerical answer.
  • Another participant suggests that the expression might be miswritten and proposes using the "Cis rule" or exponential form to simplify the problem.
  • A participant confirms the original expression and explains that |z| depends on the values of r and x, providing examples for specific values of x.
  • There is a mathematical derivation of |z| using the conjugate of z, leading to an expression involving r and x, but it is noted that it cannot be simplified to a single value.
  • One participant explains the "Cis" notation as a way to convert complex Cartesian forms to polar forms, indicating a need for further understanding of this concept.
  • A later reply expresses satisfaction with the understanding gained and suggests that the question may not have a definitive answer, reinforcing the complexity of the problem.

Areas of Agreement / Disagreement

Participants generally agree that |z| is dependent on the parameters r and x, and that it cannot be reduced to a single value. However, there is no consensus on whether the original question is valid or if it was misinterpreted.

Contextual Notes

Some participants mention the potential for simplification using trigonometric identities, but the discussion remains open-ended regarding the exact nature of the solution.

aerosmith
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if z = 2 r cos x + r i sin x
what is the value of lzl

I worked for 3 hours but yet can only find lzl in terms of r and x, but the question says find the value, can anyone help solve? this is a special question to me because i always see polar forms with coefficient of the sin and cos as the same, but this question shows otherwise.

ty, help appreciated.
 
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you sure you don't mean [tex]z = 2rCos(x) + riSin(x)[/tex] ? If so use your Cis rule or exponential equality for cos + i sin
 
sorry bout the i, i edited already, what do u mean by the cis rule or exponential equality, can u teach me?
 
can anybody help solve this for me?
 
Am I correct, that you are given z= 2r cos(x)+ i r sin(x) and want to find |z|? That will depend on r and x- it's obviously not a single number since the larger r is obviously the larger the |z|. If, for example, x= 0 then z= 2r which has absolute value 2r. If x= [itex]\frac{\pi}{2}[/itex] then z= i r and so |z|= r.

[tex]|z|= \sqrt{z\cdot\overlinez}= \sqrt{(2r cos(x)+ i r sin(x))(2r cos(x)- i r sin(x)}= \sqrt{4r^2cos^2(x)- r^2 sin^2(x)}[/= r \sqrt{4 cos^2(x)- sin^2(x)}[/tex]

You might be able to simplify that squareroot by trig identities but you can't get rid of r and x.
 
the cis thing is basically converting complex cartesian forms to polar ones

[tex]{e^{it}} = Cos(t) + i Sin(t)[/tex]

the t should be the power as well with i but for some reason the tex won't do it :( need to learn more about it i guess
 
ok, so now i know i was right, time to get to school and prove to my teacher that there is no answer, since the question asks for a value, ty ppl for helping me, i wasted 5 hours of my life working on something i got right 5 hours ago, once again ty ppl, help appreciated.
 

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