1问题呈现如图1,在△ABC中,AB=AC,∠A=20°,点E在AB上,D在AC上,∠CBD=50°,∠BCE=60°,求∠CED的度数.这就是著名的“兰利问题”.文[1]给出了两种求解途径:一是通过构造等腰三角形与等边三角形求解;二是利用正弦定理和余弦定理求解.文[2]也通过构造等边三角形求出了∠CED 1 problem is presented in Figure 1, in △ ABC, AB = AC, ∠ A = 20 °, point E in the AB, D in the AC, ∠ CBD = 50 °, ∠ BCE = 60 °, find the degree of CED This is the famous “Langley problem.” The paper [1] gives two solutions: one is to construct isosceles triangles and equilateral triangles; the other is to use sine theorem and cosine theorem to solve. 2] also obtained by constructing an equilateral triangle ∠CED