Answer
$A: 0,0 \\ B: 2c,2d \\ C: 2b,2d \\ D: 2a,0 $
Work Step by Step
An ideally placed trapezoid, which we will call trapezoid ABC, should have point A placed at the origin and side AD be on the x-axis. Calling the length of AD "2a," the x-value of C 2b, and point B (2c,2d), we obtain:
$A: 0,0 \\ B: 2c,2d \\ C: 2b,2d \\ D: 2a,0 $
Note, we double all of the numbers from last problem, for the book wants midpoints, which are equal to the length of half of a side.