Polar form?

Thread Starter

Biggsy100

Joined Apr 7, 2014
88
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
 

tjohnson

Joined Dec 23, 2014
611
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.
 

WBahn

Joined Mar 31, 2012
29,976
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
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.
 

WBahn

Joined Mar 31, 2012
29,976
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.
 

Thread Starter

Biggsy100

Joined Apr 7, 2014
88

Thread Starter

Biggsy100

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

WBahn

Joined Mar 31, 2012
29,976
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?
 

WBahn

Joined Mar 31, 2012
29,976
Where did the variable j1 come from in your first answer?
(1+2) + (j2-j3) = 3 + (j2-j3)
(1+2) - (j2-j3) = 3 - (j2-j3)

It's really no different from adding terms such as 1+x and 2-y, apart from the fact that the second number in each term is complex rather than real.
(1+2) + (x-y) = 3 + (x-y) ≠ 3 - z
(1+2) - (x-y) = 3 - (x-y) ≠ 3 - x
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.
 

WBahn

Joined Mar 31, 2012
29,976
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)
 
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