To find DH, we must find HF first. To find HF we can use Pythagorean Theorem.
(1.5)^2 + (1)^2 = HF^2
2.25 + 1 = 3.25
HF = [tex] \sqrt{13} [/tex]/2
Now we can use this length in the next application of Pythagorean Theorem for the length of DH.
(3)^2 + ([tex] \sqrt{13} [/tex]/2)^2 = DH^2
9 + 3.25 = 12.25
DH = 7/2 or 3.5in.