+128474 Triangle DBC is a 3-4-5 right triangle
So BC = 5
And AB = 20 - 5 = 15
So....since BDis parallel to AE.......we have this relationship
BC/ AB = CD/DE
5/15 = 4/DE
15/5 = DE /4
3 = DE/4 multiply both sides by 4
12 = DE
So
EC = ED + DC = 12 + 4 = 16
And by the Pythagorean Theorem,
AE = sqrt [ AC^2 - EC^2 ] = sqrt [ 20^2 - 16^2 ] = sqrt [ 400 - 144] = sqrt [ 256] = 16 ft
