1. The problem statement, all variables and given/known data In this question , I am not convinced that δAD = δAC cos theta 2. Relevant equations 3. The attempt at a solution , i think it should be δAC = δAD cos theta , am i right ? I think so because we normally get the non-vertical and non -horizontal line and then cos the angle or sin the angle to get the length in x and y direction , right ?