2. 一桁架承受外力，如圖所示。(a) 5% 試問哪些桿件為零桿，(b) 5% 求支承反力， (c) 15% 求 IJ, EJ, DE 桿件的內力。(25%)

5.如圖三所示(Figure3) Determineθand the tension in the spring, which correspond to the equilibrium position of the spring. The unstretched length of spring is h and the constant of the spring is k. The pin and roller supporters are at A and C, respectively. The point load P works on B with the downward direction and neglect the weight of all objects. (20%)