Answer
$A: (c,0); \\ C: (a,0); \\ B: (0,b)$
Work Step by Step
We know that any vertex on the x-axis has a y coordinate of 0, and we know that any coordinate on the y-axis has a x coordinate of 0. Thus, we write 0 where appropriate. Since we cannot find any relationship between the remaining points, we simply choose a new letter to write for any of the remaining blanks. This gives:
$A: (c,0); \\ C: (a,0); \\ B: (0,b)$
