1. The problem statement, all variables and given/known data Problem and worked Example 2. Relevant equations In worked example 1. Problem 3. The attempt at a solution It's the part where I'm subtracting one stress from the other stress. I put it in parenthesis on the worked example. I don't think my method here is right, I've tried to subtract each like term from the other to get my B term. When I come to extract the 3.3/8 by 3.3/8 it should be 3.3/8 - (-3.3/8) giving + 3.3/8. Also why is the radius term now divisible by the variables on the right? Can anyone see what's going on here?