Intercept d on AB and connect CD so that CD = ca.

Because ca = CD

So angle a = angle CDA

Because the angle CDA is the outer corner of the angle CDB.

So angle CDA= angle DCB+ angle CBD.

Because the angle b = x

So the angle DCB=X

So △CAD and△△△ CDB are isosceles triangles.

A: ————————

Using the exterior angle theorem of triangle