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Homework Help: Internal resistance seen by the voltage source, Vx?

  1. Dec 4, 2013 #1
    Hi everyone,

    I have attached an image of the op-amp configuration (all op-amps are ideal). Basically, the question asks to calculate the resistance seen through the voltage source. The answer is 3 kΩ but I just don't understand how this is found. If someone could assist me, I would really appreciate it.

    (By the way, I mean just resistance in the title, not internal resistance)


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    Last edited: Dec 4, 2013
  2. jcsd
  3. Dec 4, 2013 #2


    User Avatar

    Staff: Mentor

    You have labelled the current flowing in that top 1k resistor as Ix. Using the notation you have established, now mark in the magnitude and direction of the current in each of the other 4 input resistors.
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