Find the midpoint of BD.

(a/2, a/2)

Step-by-step explanation:

Coordinates of B & D are; (0, a) and (a, 0) respectively.

The formula for calculating coordinates of midpoint is;

M = ((x1 + x2)/2), ((y1 + y2)/2)

Coordinates of BD will be;

M_BD = ((0 + a)/2), ((a + 0)/2)

M_BD = (a/2, a/2)

i believe it's a.

i'm not sure on this one, most likely correct.