Starting with 2 marked points, A and B, precisely describe the straightedge and compass moves required to construct the quadrilateral ACBD in this diagram.

1.- Draw a circle from point A( A is the center of the circle)
2.- Draw a circle from point B do not change the size of the compass (B is the center of the circle)
3.- Mark the points where the two circles crosses ( C and D)
4.- Join the points ( A with C and with D, and B with C and with D).
5.- You got the quadrilateral.