So I have a question regarding the gain of common emitter amplifier. Referring to the attached diagram, the voltage gain of the circuit is -RC/RE. However, I don't understand how Vbb can be removed when completing the analysis. I've done the KCL analysis by hand and keep getting a gain function that is dependent on that value of Vbb. But the analysis completed below simply removes that Vbb. Is the analysis completed in the diagram AC analysis? Therefore the Vbb is removed since it is a constant DC value? Can anyone help clear this up? Thanks! Edit: Well it appears that I didn't read the diagram close enough. It states that lower case variables are those of changing values, which I assume means this is AC analysis. Confirmation of this would still be appreciated though.