I am trying to understand this q-point calculation. I recently asked a question about the notation used, however I now understand this.
Consider the line RB=(R1 R2)/(R1 + R2). I understand that this is the calculation of 2 parallel resistors, R1 and R2. However I do not understand what the relevance of this is in the calculation.
I have seen this from other sources, for example the last example at the bottom of this page:
Again, in this example, I understand everything until the line RB=...
How is this equation derived? I thought it might be obtained from one of Kirchoff's Laws, but if this is the case I can't see which law is used and how.
I copy the relevant diagram and calculation for convenience below.