a. By using vertical element, show that the x-centroid for the shaded area shown in Fig. la is 20 y=-x Fig. 1a b. If the triangle in Fig. Ia is cut off at the bottom to make a trapezium (blue shaded area) as shown in Fig. 1b, what is the x-centroid of the trapezium? Do not use formula for the trapezium from the appendix. y=-x- b Fig. 1b b/3