1. The problem statement, all variables and given/known data Its part B ii) and iii) that I'm stuck on. 2. Relevant equations Apparently for stationary waves, the phase difference between two particles = m(pi), where m is the number of nodes between the particles. This is according to my textbook here: 3. The attempt at a solution So following that info above from my textbook, for B ii), it should be 1 * (pi) = (pi) or 180 in degrees, 1 * (pi) follows from there being only one node between particles O and B. But I got it wrong, the answer at the back is 225 degrees. and for B iii), I'm even more confused, I done: 2 * (pi), because theres two nodes between particles O and C. So I had the answer as 2(pi) or 360 degrees. But I'm wrong, the answers at the back has it as 0 so whats going on here?