a) Find expressions for RTH and VTH at terminal a-b for the circuit of Fig. 2.1 in terms of R1, R2, R3, and Vs.
b) Repeat part (a) for the circuit of Fig. 2.2.
c) By applying the principle of superposition to Fig. 2.3, find the voltages Vab and Vcd in terms of R1, R2, R3, R4, V1, and V2.
d) For the circuit in Fig. 2.4, find an expression for the power across RL in term of VDC, R1, and RL. Find the value of RL for maximum power transfer from this equation (Hint: use calculus).