Figure h Crui se pattern AB, BA, CD, DC. 



{] and r are known; therefore, a is also known. Consider cases (a) , 

 (b) , and (c) , as follows: 



V , 



(a) If 77 cos a = + 1, then 



1 — -^cos a 

 holds. From the legs AB, BA, CD, and DC in figure 1 we have 



'AB 



1-^cos 



BA 



1 ^ 



1 + — COS 



1 sin a 



"CD 



1 ^ ■ 

 1 + — sm 



From these formulas we get 



2t\ 



(27) 



13 



