"In the isosceles trapezoid $ABCD$ with bases $AD$ and $BC$ (being $AD$ the larger base), $\angle$ABC = $2$$\angle$CDA. If $AB$ = $BC$ = $b$, the perimeter of the trapezoid is?"
I thought that this problem was very easy, but i can't figure it out. The main problem is the length of the base $AD$.
I tried with similarity of some triangles that are formed with the heights and the diagonals of the trapezoid, but nothing.