In this equation, the left-hand side would be the same linear combination as before (the ai’s are unchanged), since only the value of source yb was changed, not any of the linear elements or their placement in the circuit, The values of the circuit variables will be different due to the presence of just the single source a alone and are designated with an a superscript. x_i^a is thus the response to source a alone. If we instead kill the other source, source a, the circuit equation (4.6) becomes