5.4 Let $\triangle A B C$ be an isosceles triangle, with $\angle B$ and $\angle C$ both $80^{\circ}$. Cevians $B D$ and $C E$ divide $\angle B$ and $\angle C$ into two parts, $\angle D B C=60^{\circ}, \angle E C B=50^{\circ}$. Find $\angle E D B$.
5.4 The symmetry of isosceles triangles, here it is a rat's tail: Thus, we can try to add auxiliary lines symmetrically: draw $D F / / B C$, connect $C F$ to intersect $B D$ at $G . \triangle D F G$ is an equilateral triangle. The answer is $\angle E D B=30^{\circ}$.