Converting from Cartesian to polar form

In summary, the absolute value in complex analysis represents the modulus, so the result will be a positive real number. When converting to polar form, it is important to check which quadrant the number lies in. In this case, $1-i$ lies in the fourth quadrant, so $\theta$ will be negative. The correct polar form for $|\frac{1-i}{3}|$ is $e^{\frac{-i\pi}{4}}$.
  • #1
nacho-man
171
0
another question:

convert $|\frac{1-i}{3}|$ to polar form

i am getting $\frac{\sqrt{2}}{3} e^{\frac{i\pi}{4}}$

but the solutions say:
$e^{\frac{-i\pi}{4}}$

i did
$ x = r\cos(\theta)$ and $y=r\sin(\theta)$
so

$\frac{1}{3} = {\frac{\sqrt{2}}{3}}\cos(\theta)$
$\frac{1}{3} = \cos(\theta)$
And thus $\theta = \frac{\pi}{4}$
similarly, the same was determined for $\sin(\theta)$

What did I do wrong, why didn't i obtain a negative?
Also, is there a shorter method to find the ans? I would love if someone could give me a fully worked solution with the most efficient way to get the answer.

THanks.
 
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  • #2
nacho said:
another question:

convert $|\frac{1-i}{3}|$ to polar form

The absolute value in complex analysis represents the modulus so the result will be a positive real number.
 
  • #3
nacho said:
another question:

convert $|\frac{1-i}{3}|$ to polar form

i am getting $\frac{\sqrt{2}}{3} e^{\frac{i\pi}{4}}$

but the solutions say:
$e^{\frac{-i\pi}{4}}$

i did
$ x = r\cos(\theta)$ and $y=r\sin(\theta)$
so

$\frac{1}{3} = {\frac{\sqrt{2}}{3}}\cos(\theta)$
$\frac{1}{3} = \cos(\theta)$ This is wrong: $\color{red}{\cos\theta}$ should be $\color{red}{1/\sqrt2}$.
And thus $\theta = \color{red}{\pm}\frac{\pi}{4}$
similarly, the same was determined for $\sin(\theta)$

What did I do wrong, why didn't i obtain a negative?
Also, is there a shorter method to find the ans? I would love if someone could give me a fully worked solution with the most efficient way to get the answer.

THanks.
[I assume the mod signs should not be there, otherwise as ZaidAlyafey says the result should be a positive real number and $\theta$ will be zero.]

When converting to polar form, you should always check which quadrant the number lies in. In this case, $1-i$ is in the fourth quadrant, so $\cos\theta$ will be positive but $\sin\theta$ will be negative. This means that you should choose the negative value for $\theta$.
 
  • #4
Sorry, both typos

The absolute value shouldn't have been there, and I had the correct workings but transcribed them onto here incorrectly!

Thanks for the note about the $1+i$ lying in the 4th quadrant,
I never looked at it the correct way from the beginning! This has been my flaw up until now.

Thank you !
 
  • #5
nacho said:
Thanks for the note about the $1+i$ lying in the 4th quadrant,
just to make sure you mean that \(\displaystyle 1-i\) lying in the 4th quadrant cause \(\displaystyle 1+i\) lying in the first quadrant:P

Regards,
\(\displaystyle |\pi\rangle\)
 
  • #6
Petrus said:
just to make sure you mean that \(\displaystyle 1-i\) lying in the 4th quadrant cause \(\displaystyle 1+i\) lying in the first quadrant:P

Regards,
\(\displaystyle |\pi\rangle\)

thanks for the concern
I seem to be making typos all over the place! :P that's what I meant.

I didn't understand at first you could look at the points these way.

for instance, $1-i$ is referring to a coordinate, correct?

Yet whenever I think of coordinates, I think only in terms of $(1,-i)$ notation
 

FAQ: Converting from Cartesian to polar form

1. What is the equation for converting from Cartesian to polar form?

The equation for converting from Cartesian to polar form is: r = √(x² + y²), where r represents the distance from the origin to the point, and x and y represent the Cartesian coordinates.

2. How do you convert a point from Cartesian to polar form?

To convert a point from Cartesian to polar form, you can use the following steps:
1. Find the distance from the origin to the point using the formula r = √(x² + y²).
2. Calculate the angle θ using the formula θ = tan⁻¹(y/x).
3. The polar coordinates of the point will be (r, θ).

3. What is the difference between Cartesian and polar coordinates?

Cartesian coordinates, also known as rectangular coordinates, use a horizontal x-axis and a vertical y-axis to represent points in a two-dimensional plane. Polar coordinates, on the other hand, use a distance from the origin (r) and an angle (θ) to represent points in a two-dimensional plane.

4. Can negative values be used in polar coordinates?

Yes, negative values can be used in polar coordinates. The distance from the origin (r) can be negative if the point is in the lower half of the plane, and the angle (θ) can be negative if the point is in the left half of the plane.

5. How do you convert from polar to Cartesian form?

To convert from polar to Cartesian form, you can use the following equations:
x = r cosθ and y = r sinθ.
Simply plug in the values for r and θ to find the corresponding Cartesian coordinates.

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