An outer angle of a triangle is equal to the sum of two non-adjacent inner angles, and the corresponding sides of BDE, CEF, BDE, CEF, BD, CE, ASA and congruent triangles are equal.

At this time, the ship did not deviate from the course.

6. (1) △ EAD△, where ∠EAD =∞,;

(2) ;

(3) The law is: ∠1+∠ 2 = 2 ∠ a.