Finding polar form of complex number

In summary, when converting complex numbers to polar form, there may be two different angles that have the same sin value. It is important to determine which angle is correct by considering the values of cos and choosing the one that matches the given complex number.
  • #1
astrololo
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3

Homework Statement


I have the following complex numbers : -3,18 +4,19i
I must put it in polar form.

Homework Equations


r=(a^2+b^2)^(1/2)
cos x = a/r
sin x = b/r

The Attempt at a Solution



I was able to find with cos x = a/r that the x = 127,20

But when I do it with sin x = b/r I obtain like 52 degrees. I know that I Must obtain 127,20 for BOTH. Why isn't it working ?
 
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  • #2
The sin of both those angles are the same, so you must decide which is correct. That is the angle that has the correct a,b values. 52 degrees would be at (3.18, 4.19) and 127.2 degrees is at (-3.18, 4.19).
 
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  • #3
FactChecker said:
The sin of both those angles are the same, so you must decide which is correct. That is the angle that has the correct a,b values. 52 degrees would be at (3.18, 4.19) and 127.2 degrees is at (-3.18, 4.19).

Oh ok so its normal that I obtain two different values. Ok then, thank you!
 
  • #4
Yes, There are always two values of [itex]\theta[/itex] in the interval 0 to [itex]2\pi[/itex] that have the same [itex]sin(\theta)[/itex]. But you still have to determine which is correct for the specific problem- the two different values, [itex]\theta[/itex] have different values for [itex]cos(\theta)[/itex].
 

Related to Finding polar form of complex number

1. What is the polar form of a complex number?

The polar form of a complex number is a way of representing a complex number in terms of its magnitude (or modulus) and its argument (or angle). It is expressed in the form r(cosθ + isinθ), where r is the modulus and θ is the argument.

2. How do you convert a complex number to polar form?

To convert a complex number to polar form, you can use the formula r = √(a² + b²) to find the modulus, where a and b are the real and imaginary parts of the complex number, respectively. Then, you can use the formula θ = tan⁻¹(b/a) to find the argument. Finally, the polar form can be written as r(cosθ + isinθ).

3. What is the difference between polar form and rectangular form?

The main difference between polar form and rectangular form is the way they represent a complex number. Rectangular form is expressed in the form a + bi, where a and b are real numbers, while polar form is expressed in the form r(cosθ + isinθ), where r is the modulus and θ is the argument.

4. How do you graph a complex number in polar form?

To graph a complex number in polar form, you can use the modulus and argument to determine the coordinates of the point on the complex plane. The modulus represents the distance from the origin, and the argument represents the angle from the positive real axis in a counterclockwise direction. You can then plot the point on the complex plane.

5. What are the advantages of using polar form for complex numbers?

One advantage of using polar form for complex numbers is that it provides a geometric interpretation of the number. The modulus gives the magnitude of the number, while the argument gives the direction. This can be useful in understanding the properties of complex numbers and their operations. Additionally, polar form can also make calculations involving complex numbers easier, especially when dealing with powers and roots.

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