A rectangular sheet of paper, ABCD has `AD=1cm and AB=rcm`, where `1 < r < 2.` The paper is folded along a line through A so that the edge AD falls onto the edge AB. Whithout unfolding, the paper is folded again along a line thruogh B so that edge CB also lies on AB. the result is a triangular piece of paper. A region of the triangle is four sheets thich. In terms of r, what is the area of this regions?