Maths問題-Deductive Geometry

(a) Triangle DEK similar to triangle KBC, so DE/DK = BC/KC, 4/2 = a/5, a= 10.
BK/KC = KE/DK , so b/5 = 3/2, b = 7.5
Triangle ADE similar triangle ABC, so AD/DE = AB/BC, 5/4 = (5 + c)/a
5/4 = ( 5 + c)/10 , 50 = 20 + 4c, 4c = 30, c = 30/4 = 7.5
(b)
triangle ADE similar to triangle ABC, so AD/AE = AC/AB, 8/10 = 12/(8 + d)
64 + 8d = 120, 8d = 56, d = 7.