Final answer:
The forces in members DB and DC of the cantilever truss are both 300 N. Member DB is in tension, while member DC is in compression.
Step-by-step explanation:
To determine the forces in members DB and DC, we need to analyze the forces acting on the cantilever truss. Since a 300 N force is applied at point A, there will be an equal and opposite force of 300 N acting at point B. This force along member DB creates tension in the member. The forces in member DC can be determined by considering the equilibrium of forces at point C. Since there are no external horizontal forces acting on the truss, the horizontal component of the force in member DC must equal the horizontal component of the force in member DB. Therefore, the force in member DC is also 300 N, and it creates compression in the member.