On side AB construct equilateral △ABE and △ABE' where E is in the interior of ∠BAD.

On side AD construct equilateral △ABF and △ABF' where F is in the interior of ∠BAD.

1) Prove points {C,E,F'} are collinear as well as {C,E',F}

2) Prove △CEF and △CE'F' are equilateral.