Answer:
F. 8
Explanation:
The ratio of the long side to the short side is the same in similar triangles. The long side of triangle BAD is AD, which has length 20-4 = 16.
BD/DE = AD/BD
h/4 = 16/h
h^2 = 64 . . . . . . . multiply by 4h
h = 8 . . . . . . . . . . take the square root (matches selection F)
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Comment on this geometry
BD = √(AD·DC) is called the "geometric mean" of the segments AD and DC. This geometry has some other geometric mean relationships as well:
BC = √(AC·DC)
BA = √(AC·AD)