Solve {c}{Q_{D}=-8P_{D}+20}{Q_{S}=9P_{S}-8}

$$\left. \begin{array} { c } { Q _ { D } = - 8 P _ { D } + 20 } \\ { Q _ { S } = 9 P _ { S } - 8 } \end{array} \right.$$

Solve for Q_D, P_D, Q_S, P_S (complex solution)

$$Q_{D}=20-8P_{D}$$

$$P_{D}\in \mathrm{C}$$

$$Q_{S}=9P_{S}-8$$

$$P_{S}\in \mathrm{C}$$

Solve for Q_D, P_D, Q_S, P_S

$$Q_{D}=20-8P_{D}$$

$$P_{D}\in \mathrm{R}$$

$$Q_{S}=9P_{S}-8$$

$$P_{S}\in \mathrm{R}$$