Was quizzed over something that wasn't in a video. Any help on what the question means?

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Macy Kozak

1 septembre 2018 00:57

Hi! My name's Macy. Been doing Algebra II - Complex numbers (as well as the imaginary part), and I was asked the question what is z1 (with the one being placed lower) minus z2 (again with the 2 going lower). This wasn't in any of the videos I've seen in this unit. On top of it, there is no clear answer on any part of the internet. Would look it up in my GED books, but I don't learn the best that way and feel it wouldn't work. Can someone tell me -specifically- where to find /something/ on this subject or can someone please add it to the videos relevant to/within the lesson?

The problem:

https://farm2.staticflickr.com/1874/29457888777_b9a9699cc9_b.jpg

Links to the videos concerning this lesson:

https://www.khanacademy.org/math/algebra2/introduction-to-complex-numbers-algebra-2/the-complex-plane-algebra-2/v/plotting-complex-numbers-on-the-complex-plane

https://www.khanacademy.org/math/algebra2/introduction-to-complex-numbers-algebra-2/adding-and-subtracting-complex-numbers-algebra-2/v/adding-complex-numbers

https://www.khanacademy.org/math/algebra2/introduction-to-complex-numbers-algebra-2/adding-and-subtracting-complex-numbers-algebra-2/v/subtracting-complex-numbers

The correct answer:

https://farm2.staticflickr.com/1900/42566015370_c1ca28684a_b.jpg

It has the complex number minus the complex number situation, however, I fail to see where it goes over anything to do with the materials of the question itself. Don't think it was in the unit either. Unless I'm not seeing it, in which case my apologies.

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4 commentaires

Lisa Krueger

13 septembre 2018 16:46
1

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Hello Macy! I'm sorry you are frustrated with Khan Academy. When you used the hints did you use all the hints? I did a similar problem of z1 + z2 (see image below) and it walked me through the entire problem.

Please let me know if you have any further questions, comments, or suggestions. Thank you for posting.
Macy Kozak

13 septembre 2018 23:14
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I saw that, but that wasn't in /any/ of the videos leading up to this unit or lesson. I shouldn't have to get a problem wrong and check an answer to figure what is being asked of me. On top of it, Z clearly has some sort of set value. This means that if I run into them again with anything other then a 1 & 2 lower exponent...I'm not going to know what to do again.
Regina Litman

14 septembre 2018 02:19
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z (lower case) is a convention for designating a complex number, often found in higher mathematics, similar to x (also lower case) being used for real numbers in subjects such as Algebra 1.

z with the 1 below it (the 1 is known as a subscript) and z with the 2 below it are ways of specifying multiple complex numbers. Sometimes x is shown this way (with the 1s and the 2s) for multiple real numbers.

Example: Suppose z1 = 2 + 4i and z2 = 3 - i. z1 minus z2 would then be 2 + 4i - (3-i) = 2 + 4i - 3 + i = -1 + 5i.
Macy Kozak

14 septembre 2018 03:44
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That helps, thank you so much!

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Was quizzed over something that wasn't in a video. Any help on what the question means?

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