Algebra help with complex numbers

In summary, the conversation discusses the goal of solving for t in an equation with constants R, C, and ω. The equation is in the form of cos(ωt) = 1 - e^(-t/RC) and the attempt at a solution involves converting the cosine term to complex notation and rearranging the equation, but no closed-form solution is expected and numerical or approximation methods may need to be used.
  • #1
iScience
466
5

Homework Statement



goal: solve for t; all else are constants

$$cos(\omega t)=1-e^{-(\frac{t}{RC})}$$

Homework Equations



none

The Attempt at a Solution



i turned the cos to complex notation & rearranged

$$e^{i\omega t}+e^{-(\frac{t}{RC})}=1$$

$$ln(e^{i\omega t}+e^{-(\frac{t}{RC})})=0$$

and i am stuck..
 
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  • #2
iScience said:

Homework Statement



goal: solve for t; all else are constants

$$cos(\omega t)=1-e^{-(\frac{t}{RC})}$$

If you know values for ##R,~C,~\omega## you can solve it numerically. Otherwise you are out of luck.
 
  • #3
iScience said:

Homework Statement



goal: solve for t; all else are constants

$$cos(\omega t)=1-e^{-(\frac{t}{RC})}$$

Homework Equations



none

The Attempt at a Solution



i turned the cos to complex notation & rearranged

$$e^{i\omega t}+e^{-(\frac{t}{RC})}=1$$

$$ln(e^{i\omega t}+e^{-(\frac{t}{RC})})=0$$

and i am stuck..

No wonder you are stuck: ##e^{i \omega t} \neq \cos(\omega t)##. Besides that, I doubt very much that your equation possesses a closed-form solution. You will probably need to resort to approximations, or to numerical solutions for known numerical values of your input constants.
 
  • #4
Just looking at the form of the original equation, how many solutions do you expect and roughly where?
 

FAQ: Algebra help with complex numbers

What are complex numbers?

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

How do I add or subtract complex numbers?

To add or subtract complex numbers, you simply add or subtract the real and imaginary parts separately. For example, (2 + 3i) + (4 + 2i) = (2 + 4) + (3 + 2)i = 6 + 5i.

How do I multiply complex numbers?

To multiply complex numbers, you can use the FOIL method just like with binomials. For example, (2 + 3i)(4 + 2i) = 2(4) + 2(2i) + 3i(4) + 3i(2i) = 8 + 4i + 12i + 6i^2 = -2 + 16i.

How do I divide complex numbers?

To divide complex numbers, you have to rationalize the denominator. This means multiplying the top and bottom by the conjugate of the denominator. For example, (4 + 2i) / (2 - 3i) = (4 + 2i)(2 + 3i) / (2 - 3i)(2 + 3i) = (8 + 12i + 4i + 6i^2) / (4 + 9i^2) = (2 + 16i) / 13 = 2/13 + (16/13)i.

How is complex algebra used in real life?

Complex algebra is used in various fields of science and technology, such as engineering, physics, and computer science. It is also used in financial analysis and in creating mathematical models for real-life situations. For example, complex numbers are used in electrical engineering to represent the impedance of a circuit, and in computer graphics to represent 3D rotations and transformations.

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