I had no clue how to do this and could only grasp the first basic parts but even then i couldn't get it right and in the end i had to look at the answer, which confused me even more. So i was wondering if anyone else understands this, and if so could you describe it in words please? 1. The problem statement, all variables and given/known data 2. Relevant equations As above 3. The attempt at a solution I understand the first part, getting cos B from the graph...yet when it gets to the other part '...angle in the bottom right hand corner of the triangle is PI - A...' i don't understand how they came to that...but i was wondering, the sin (PI/2 - A) seems to be related to a trigonometric identity? If someone could explain it that would be great.