The markets for Good X and Good Y are initially in equilibrium at price P1 P_1\,P1 and quantity Q1Q_1Q1. If the supply of Good X decreases (shifting from S1 S_1\,S1 to S2S_2S2) and both markets move to a new equilibrium at P2 P_2\,P2 and Q2 Q_2\,Q2 as shown below, it can be concluded that Good X and Good Y are in:

competitive demand.
joint demand.
derived demand.
composite demand.