
Since BD is the bisector of the angle ∠CBA, it follows that ∣CD∣:∣AD∣=∣BC∣:∣AB∣, and because of that ∣CE∣∣CD∣=∣AD∣∣CD∣=∣AB∣∣BC∣=∣CA∣∣CB∣.
Triangles ABC and EDC have a common angle in vertex C and equal ratios of corresponding sides so they are similar. Hence ∠CED=∠CAB.
Let ∠ABC=2x. Then ∠CBD=∠DBA=x and ∠ACB=2x. Furthermore, ∠CED=∠BAC=180∘−4x.
Since the triangle BED is isosceles, we have ∠DEB=90∘−2x. As ∠DEB+∠CED=180∘, we get
(90∘−2x)+(180∘−4x)=180∘,
whence follows x=20∘. The angles of the observed triangle are ∠ABC=∠ACB=40∘ and ∠BAC=100∘.