sen p + sen q = 2 . sen ( p+q / 2) . cos ( p – q /2)

sen p – sen q = 2 . sen ( p - q / 2) . cos ( p + q /2)

cos p + cos q = 2 . cos ( p+q / 2) . cos ( p – q /2)

cos p + cos q = 2 . sen ( p+q / 2) . sen ( p – q /2)