# Thread: Help with vector/degree math

1. ## Help with vector/degree math

I just looked at the homework due tomorrow for my circuits class and it looks like a review of vector and degree math. I don't remember how this is done or what exactly is being asked. I believe I have to convert degrees to another value. Could someone give me some guidance on what to do? Thanks.

The (angle symbol) is supposed to be a symbol for an angle because I didn't know how to denote it on the forum.

Find A+B, A-B, AB, A/B, and 1/A if:
1) A= 8 + j2 B= 5 - j4

2) A= 10*(angle symb) 45 degrees B= 9*(angle symb) 30 degrees

3) A= 7*(angle symb) -40 degrees B= 6-j2

2. Originally Posted by nafix
I just looked at the homework due tomorrow for my circuits class and it looks like a review of vector and degree math. I don't remember how this is done or what exactly is being asked. I believe I have to convert degrees to another value. Could someone give me some guidance on what to do? Thanks.

The (angle symbol) is supposed to be a symbol for an angle because I didn't know how to denote it on the forum.

Find A+B, A-B, AB, A/B, and 1/A if:
1) A= 8 + j2 B= 5 - j4

2) A= 10*(angle symb) 45 degrees B= 9*(angle symb) 30 degrees

3) A= 7*(angle symb) -40 degrees B= 6-j2
Note: j is a common engineering symbol for $\sqrt{-1}$. Complex numbers are used extensively in circuit theory - the symbol i is therefore not used because of confusion with the symbol i for current.

You're dealing with the arithmetic of complex numbers.

In 2):
$A = 7 \angle (-40^0)$ is an equivalent way of writing $10 \text{cis} (-40^0) = 10 (\cos(-40^0) + j \sin (-40^0) )$.

$A = 9 \angle (30^0)$ is an equivalent way of writing $9 \text{cis} (30^0) = 9 (\cos(30^0) + j \sin (30^0) )$.

The former is the polar form of a complex number, the latter is the Cartesian form.

If you have no memory of this material then I'm sorry but I have bad news - you need to extensively review your notes, textbook, on-line lectures notes etc.

If you have nothing to refer to (which I doubt very much) then you might start by reading the first two sections of this. Note that the symbol i rather than j is usually used out side of the engineering fraternity. There is no doubt plenty of other review resources on-line, google is your friend. Alternatively, another member might have the time and inclination to provide a step-by-step review of this material for you. A search of this forum will probably turn up plenty of useful examples as well.

3. Thankyou for your help. I had missed the past couple lectures and was mistaking j for a vector notation rather than a complex number.