MathNet 2026 — Part 03 Question 72

On a straight line we have four points $A, B, C$ and $D$, in that order, so that $A B = C D$. $E$ is a point off the line such that $C E = D E$. It shows that $\angle C E D = 2 \angle A E B$ if and only if $A C = E C$.