计算悬臂梁A点的挠度，分别采用(a)材料力学的梁理论，(b)8个三角形单元，(c)4个矩形单元和(d)1个8结点等参数单元的方法-Calculate the deflection of the cantilever point A, respectively (a) mechanics of materials beam theory, (b) 8 triangle units, (c) 4 rectangle units and (d) 1 8-node element method and