Plan the Solution  
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The figure shows a rigid bar A B C D pinned at A and supported by vertical bars at B and C. The vertical bar at B is labeled 1 and pinned at its top end and the vertical bar at C is labeled 2 and pinned at its bottom end. The separation between A and B is 760 millimeters. The separation between B and C is 760 millimeters and the separation between C and D is 120 millimeters. A load P directed vertically downwards is applied at D. To solve this problem, a five-step procedure will be used.

Step 1 – Equilibrium equation

Draw a free-body diagram (FBD) of the rigid bar. Assume tension forces in members (1) and (2). Write a moment equilibrium equation about the pinned support at A.