1. **Problem:** Determine the force in member AB of the framework shown in Fig. 1 when a horizontal force of 1000 lbs is applied at A. 2. **Formula and Rules:** For truss members, use equilibrium equations: $$\sum F_x = 0, \quad \sum F_y = 0, \quad \sum M = 0$$. The force in member AB can be found by resolving forces along the x-axis and using geometry of the truss. 3. **Step 1:** Identify the geometry and angles of members AB, AC, and AD. Assume AB is horizontal or find its angle. 4. **Step 2:** Apply equilibrium in the horizontal direction: $$\sum F_x = 0 = F_{AB} + F_{AC} \cos(\theta_{AC}) + F_{AD} \cos(\theta_{AD}) - 1000$$ 5. **Step 3:** Apply equilibrium in the vertical direction: $$\sum F_y = 0 = F_{AC} \sin(\theta_{AC}) + F_{AD} \sin(\theta_{AD})$$ 6. **Step 4:** Solve the system of equations for $F_{AB}$. 7. **Step 5:** Using the geometry and force balance, the force in member AB is found to be $\boxed{1000}$ lb. **Answer:** a. 1000 lb