Chapter 10 - Section 10.3 - Preparing to Do Analytic Proofs - Exercises - Page 473: 15

$A: 0,0 \\ B: a, 0 \\ C: a-c, d \\ D: c,d$

We call the point A at the origin, which is $(0,0)$. We call the length of the first base a, making B the point: $(a,0)$. We are told that point D is $(c,d)$. We find point C: $(a-c, d)$.