找到正確的輔助線用了約兩天時間。剩下的工作用了大約半天。整理到目前的條理用了一個多小時。最近幾天的早鍛煉（走路約50分鐘）都在考慮這道題目。

Let ∆ABC = S.

Choose F in AB so that ED//CF. In ∆ACF,

sin ∠A/CF = sin(∠ACF)/AF

i.e.

CF/sin(45°) = AF/sin(75°)

Because ∠B = 30° and ∠CFB = 120°, CF = BF。

BF/AF = sin(45°)/ sin(75°) = sqrt(3) – 1

∆BCF/∆ACF = BF/AF = sqrt(3) – 1

∆ACF = S/sqrt(3) (by ∆ACF+∆BCF=S)

∆AED/∆ACF = sqrt(3)/2 = (AD/AF)^2 (by ∆AED=S/2)

AD/AB = AD/(AF+BF) = (AD/AF)/(1+BF/AF)

= (AD/AF)/sqrt(3) =12^(-1/4)