The circuit diagram shows a low-cost 3-input video MUX cable driver. In this circuit, the amplifier is loaded by the sum of RF and RG of each disabled amplifier. Resistor values have been chosen to ...

Now, the thing to remember is that we are using a CD4512 chip, whose truth table is shown below. The important thing to note here is that, in addition to the three multiplexer select controls, A, B, ...