The three sides of triangle $a < b < c$ are in arithmetic progression (AP) with common difference $d = b - a = c - b$. Denote the angles opposite to sides $a , b , c$ respectively by $A , B , C$.
\textbf{Statements}
(1) $d$ must be less than $a$.\\
(2) $d$ can be any positive number less than $a$.\\
(3) The numbers $\sin A , \sin B , \sin C$ are in AP.\\
(4) The numbers $\cos A , \cos B , \cos C$ are in AP.