• Support PF! Buy your school textbooks, materials and every day products Here!

Imaginary fraction questions. lost.

  • Thread starter ahhgidaa
  • Start date
  • #1
11
0
im studying for my circuits midterm and the proff has handouts with questions and answers but not detailed answers. i cant figure out how he went from a fraction to an answer.

(-j2)(2+j2)/-j2+2+j2 the answer on the paper is 2-j2


i do not know what im allowed to do with the 2 next to the j with the distributive properties.


another example i was stuck on was i= -j2/1+j the answer here was rad2 at an angle of -135

and the above equation came from -j2+(2-j4) I_2 + (I_1 + I_2)j6=0 with I_1 =1

and insight or help would be appreciated. thakns
 

Answers and Replies

  • #2
33,269
4,966
im studying for my circuits midterm and the proff has handouts with questions and answers but not detailed answers. i cant figure out how he went from a fraction to an answer.

(-j2)(2+j2)/-j2+2+j2 the answer on the paper is 2-j2
First off, you need to learn how to write mathematical expressions so that they mean what you intend. I am willing to bet that on the handout it looks like this:

[tex]\frac{-2j(2 + 2j)}{-2j + 2 + 2j}[/tex]

If you write fractions like this without using LaTeX to format them, put parentheses around the entire numerator and the entire denominator.

If you write 2j, people will be likely to mistake this for j2, which is something different.

For this problem, the first thing to do is to simplify the denominator.
i do not know what im allowed to do with the 2 next to the j with the distributive properties.


another example i was stuck on was i= -j2/1+j
I'm guessing you mean i = -2j/(1 + j).

Look for an example where they rationalize the denominator by multiplying by the conjugate over itself.
the answer here was rad2 at an angle of -135

and the above equation came from -j2+(2-j4) I_2 + (I_1 + I_2)j6=0 with I_1 =1

and insight or help would be appreciated. thakns
 
  • #3
11
0
i ended up with -2j-j^2 which i^2 is -1 so i finally got the answer 2-2j and i copied it exactly how it was but ure way of putting it help me with the math. idk why he writes it like that
 
  • #4
HallsofIvy
Science Advisor
Homework Helper
41,806
932
1) Don't mix "j" and "i".

2) -2j- i^2= 1- 2j, not 2- 2j.

3) I think Mark44 meant to say that some would confuse "j2" with "j^2", not "2j".
 
  • #5
33,269
4,966
1) Don't mix "j" and "i".
The OP is in an electronics class - they write j for the imaginary unit, probably because i is used for electrical current. Still, the advice is good. Use one or the other consistently, but don't use both.
2) -2j- i^2= 1- 2j, not 2- 2j.

3) I think Mark44 meant to say that some would confuse "j2" with "j^2", not "2j".
Right, that's exactly what I meant.
 

Related Threads on Imaginary fraction questions. lost.

  • Last Post
Replies
3
Views
990
Replies
18
Views
900
  • Last Post
Replies
14
Views
2K
  • Last Post
Replies
1
Views
1K
  • Last Post
Replies
2
Views
2K
  • Last Post
Replies
2
Views
1K
  • Last Post
Replies
14
Views
888
  • Last Post
Replies
3
Views
851
  • Last Post
Replies
17
Views
775
  • Last Post
Replies
3
Views
2K
Top