Algebra help, Kirchoffs rule problem.

[jKotha]

Hey guys, I'm having a little trouble with some basic algebra. I'm working on solving for currents using kirchhoffs rule.

4E/R - 9I3/2 = I3

Trying to solve for I3... I should get:
8E/2R -9I3 = 2(I3).. and then 8E/2R = 11(I3).. and then I3= 4E/11R

However I am looking at my teachers solution and her answer was:

4E/R - 9I3/2 = I3
4E/R = 2I3/2 + 9I3/2 = 11I3/2 . How did she get the 2I3/2? It doesn't make sense to me. Once again, I am trying to solve for I3.

Please help, I really appreciate it. Thanks.

 

[robb_]

Look at your first equation again. You did two things in that equation. There is your error.

 

[jKotha]

I don't understand..

How did I do 2 things?
If I'm left with 8E/2R = 11(I3), then finding I3 would be dividing both sides by 11, which would not give me the correct answer.

Also, that doesn't explain where she got the 2I3/2 on the right side. Thats what I'm concerned about.

Still stuck, thanks for the help, but I don't quite understand it.

 

[robb_]

How did you go from - 9I3/2 to -9I3?

 

[jKotha]

I multiplied both sides of the equation by 2.

 

[robb_]

Did you multiply each term by 2?

 

[jKotha]

yes..

4E/R - 9I3/2 = I3

x 2

8E/2R - 9I3 = 2I3

 

[jKotha]

Nevermind..
I"m stupid.. I figured it out.

Thanks man.

 

[robb_]

4*2=8. right?

 

[robb_]

no problem friend