# Polar form?

Discussion in 'Math' started by Biggsy100, Jun 9, 2015.

1. ### Biggsy100 Thread Starter Member

Apr 7, 2014
88
1
If A=1+j2 and B+2-J3, Find by calculation the magnitude and argument of the following complex numbers, stating each result in polar form:

(i) A+B = (1+j2) + (2-j3)

Is this where I cross multiply with first brackets and 2nd brackets....so 1 x 2 + 2 x6 2x2 +2 x 6 to get my answer

I also have A - B , A x B , A/B

2. ### Papabravo Expert

Feb 24, 2006
10,338
1,850
I don't think so.
A + B = (1 + 2) + (j2 - j3) = 3 -j1
You try A - B

3. ### tjohnson Active Member

Dec 23, 2014
618
122
Adding real and complex numbers together is like adding apples and oranges. Therefore, it is impossible to add terms such as 1 and j2 or 2 and -j3. However, you can add terms of the same sort together the way Papabravo showed.

4. ### Biggsy100 Thread Starter Member

Apr 7, 2014
88
1
? Ok, so it's as simple as moving the j over?

5. ### tjohnson Active Member

Dec 23, 2014
618
122
Last edited: Jun 9, 2015
6. ### WBahn Moderator

Mar 31, 2012
18,079
4,917
This looks like homework. Is it. If so, it is better placed in the Homework Help forum where it will get more attention than in the Math forum. If it's homework, I can move it.

7. ### Biggsy100 Thread Starter Member

Apr 7, 2014
88
1
This is a nightmare, that's what it is... . It's actually an assignment that I missed on my course.

8. ### WBahn Moderator

Mar 31, 2012
18,079
4,917
What is the course? Are you supposed to just be learning about complex numbers, or are you supposed to already be familiar with them at this point? If the latter, then you will really need to look at some of those resources that have been linked in your various threads.

Apr 7, 2014
88
1
10. ### Biggsy100 Thread Starter Member

Apr 7, 2014
88
1
(
HND - Analytical methods for Engineers

11. ### WBahn Moderator

Mar 31, 2012
18,079
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I have no idea what that course entails and what the prerequisites are. So is it assumed that you have never seen complex numbers before taking this course or not?

12. ### Biggsy100 Thread Starter Member

Apr 7, 2014
88
1
You 'Assumed' right

13. ### WBahn Moderator

Mar 31, 2012
18,079
4,917
I didn't assume anything, I asked about what assumption the course makes regarding your prior knowledge of complex numbers. And since the question was duel ended (the "or not" at the end), it doesn't have a "yes" or "no" answer. So let me make it a yes or no question.

Is this course taught based on the assumption that the students have never seen complex numbers before?

14. ### Biggsy100 Thread Starter Member

Apr 7, 2014
88
1
not sure ...I am a student not a teacher!

15. ### WBahn Moderator

Mar 31, 2012
18,079
4,917
Here j2 and j3 are not the names of two identifiers. It is j·2 and j·3 where j is the imaginary constant. So (j2 - j3) = -j1.

Personally I prefer putting the imaginary constant after the coefficient, but that's a matter of style.

tjohnson likes this.
16. ### WBahn Moderator

Mar 31, 2012
18,079
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Still, you should be able to explain why you did what you did based on your present understanding of the material. Otherwise you are just mimicking a monkey that is mimicking the instructor.

17. ### Papabravo Expert

Feb 24, 2006
10,338
1,850
Not quite
A - B = (1 + j2) - (2 -j3) = (1 - 2) - (j2 - j3) = -1 - j1

18. ### WBahn Moderator

Mar 31, 2012
18,079
4,917
To show you what I mean, you should be able to apply normal algebra skills to factor out the j (remember, it's just a constant!)

(1 + 2) + (j2 - j3) = (1 + 2) + j(2 - 3) = 3 + j(-1) = 3 - j1

Use that same process for (1+2) - (j2 - j3)