MathNet 2022-part-04 — 197 problems (EN–VI) Question 183

Given an equilateral triangle $ABC$. Points $D$, $E$, $F$ lie on sides $BC$, $CA$, $AB$, respectively, and satisfy $AF = BD$ and $DF = EF \neq DE$. Prove that $\angle CDE = 90^\circ$.