$D$ is a point inside $\triangle ABC$, $\angle CAD=\angle DAB=10$, $\angle CBD=40$, $\angle DBA=20$, what is $\angle CDB$? $D$ is a point inside $\triangle ABC$, $\angle CAD=\angle DAB=10$, $\angle CBD=40$, $\angle DBA=20$, what is $\angle CDB$?
I'm sure I'm supposed to use trigonometry to obtain the value of $\angle CDB$ but I'm not exactly sure how to start. Maybe Law of Sines?

Take E, reflection of B in AD; it belongs to AC and $\triangle BED$ is equilateral; easily BE=BC, BEC being a Langley triangle and required $\widehat{BDC}=70^\circ$.
