. Let ABCD be the trapezoid below. You are given that DA = a, AB = 5, and DC = 25, as demonstrated in the diagram. The point E is the midpoint of AC, and the point F is the midpoint of BC. The midpoint of a line segment is, as the name suggests, the middle point between the two ends of the line segment. A B F E C 25 D (a) Write each of the vectors DB, AC, and BC as a linear combination of a and b. (b) Show that EF is parallel to DC.