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    pop000's Avatar
    pop000 Posts: 352, Reputation: 6
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    #1

    Nov 18, 2011, 07:41 AM
    find the resistance of CD (Rcd)
    in the picture you can what I did till I stuck.

    NO.1 is the source, and NO.2 is after I found the equivalent resistance R-5,6,7 (which is in parallel).

    but now I think R2 and R1 is also parallel but I am not sure.

    all I know that is the final answer should be Rcd=3-ohm

    thanks.
    ebaines's Avatar
    ebaines Posts: 12,130, Reputation: 1307
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    #2

    Nov 18, 2011, 08:52 AM
    Quote Originally Posted by pop000 View Post
    in the picture you can what i did till i stuck.
    Pop - you need to attach the figure.
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    #3

    Nov 18, 2011, 08:59 AM
    Oh again is happened sorry :)
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    ebaines Posts: 12,130, Reputation: 1307
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    #4

    Nov 18, 2011, 09:32 AM
    The dead short can be thought of as a 0-ohm resistor in parallel with the 6 ohm. That makes the combination equivalent to 0 ohms. So now you have R2 and R1 in parallel, the combination of which is in series with R3.

    I see that in figure 1 you have R2= 3 ohms, but in figure 2 you show R2 = 9 ohms. Which is it?
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    #5

    Nov 18, 2011, 09:46 AM
    "I see that in figure 1 you have R2= 3 ohms, but in figure 2 you show R2 = 9 ohms. Which is it?"

    well in both R2=9ohm and R1=3ohm.where I show R2=3 ohm?


    well so if you told that I have R2 and R1 in parallel, the combination of which is in series with R3.

    so I get R:2,1=9*3/9+3=2.25-ohm,now we know is in series with R3 so we get 2.25+1.5=3.75-ohm

    do I correct till here ?
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    #6

    Nov 18, 2011, 09:52 AM
    ohh yes yes now I see it, my mistake OK I solve it now.

    so yes R2=3.


    so I get R:2,1=3*3/3+3=1.5-ohm,now we know is in series with R3 so we get 1.5+1.5=3.00-ohm

    so Rcd=3-ohm this is the final answer.

    sorry for the confusion.

    really thanks for your help :)
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    ebaines Posts: 12,130, Reputation: 1307
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    #7

    Nov 18, 2011, 09:59 AM
    Quote Originally Posted by pop000 View Post
    well in both R2=9ohm and R1=3ohm.where i show R2=3 ohm?
    You show R2 = 3 ohms in the upper (see attached snippet):

    Quote Originally Posted by pop000 View Post
    so i get R:2,1=9*3/9+3=2.25-ohm,now we know is in series with R3 so we get 2.25+1.5=3.75-ohm

    do i correct till here ?
    Yes. However, if R2 = 3 ohms then you fget a final answer of Rcd -= 3 ohms.
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    #8

    Nov 18, 2011, 11:24 AM
    Yes you are correct it was my mistake :)

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