It is so wonderful that there are such "theoretical questions" that make us think and reveal the ideas behind mysterious circuits.

When I read this question, my knee-jerk reaction was that this is impossible. But the problem remained dormant in my head, and at some point I began to make a connection with the somewhat strange circuit of an *amplifier with a T-bridge in the negative feedback*.

Basic idea
==========

... is extremely simple: According to Ohm's law, the current flowing through a resistor R with applied voltage V across it is I = V/R. If we actually supply the resistor with, for example, ten times lower voltage, the current will also decrease ten times (I = V/10R) and it will appear that the resistance has increased ten times (R = 10V/R).

Of course, there is a "small" catch here (as in any circus trick:-) - ***we see the voltage V when actually a voltage of V/10 is applied***.


Implementation
==============

Ohm's circuit with true 10 k resistance
-----------------

As an example, the current flowing through a 10 k resistor R with applied 10 V voltage V across it is I = 1 mA. We know that the resistance is 10 k but we can also measure the current and calculate the resistance - R = V/R = 10 V/1 mA = 10 k.

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![schematic](https://i.sstatic.net/GhdSX.png)

<!-- End schematic -->

[![STEP 1][1]][1]

Inverting amplifier with true 10 k R2
-----------------

As another example, the 10 k resistor R2 and R1 set a gain of -1 of an op-amp inverting amplifier.

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![schematic](https://i.sstatic.net/Oyb7A.png)

<!-- End schematic -->

[![STEP 2][2]][2]

Ohm's circuit with virtual 100 k resistance
-----------------

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![schematic](https://i.sstatic.net/mIJmc.png)

<!-- End schematic -->

[![STEP 3_1][3]][3]

[![STEP 3_2][4]][4]

Inverting amplifier with virtual 100 k R2
-----------------

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![schematic](https://i.sstatic.net/TCq5z.png)

<!-- End schematic -->

[![STEP 4_1][5]][5]

[![STEP 4_2][6]][6]

Inverting amplifier with *T bridge* instead R2
-----------------

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![schematic](https://i.sstatic.net/iZumt.png)

<!-- End schematic -->

[![STEP 5][7]][7]


  [1]: https://i.sstatic.net/sBYk3.png
  [2]: https://i.sstatic.net/S6sFy.png
  [3]: https://i.sstatic.net/14vTT.png
  [4]: https://i.sstatic.net/4k4QE.png
  [5]: https://i.sstatic.net/xfiUA.png
  [6]: https://i.sstatic.net/Y0kAG.png
  [7]: https://i.sstatic.net/T07LS.png