1. The problem statement, all variables and given/known data 2. Relevant equations p.q+p.r 3. The attempt at a solution I've expanded p.(q+r) to give p.q+p.r. The magnitude of p is 3, and since ABE is an equilateral triangle, the magnitude of q is also 3, right? So then p.q=9, but the answer scheme states that p.q=4.5. I'm still pretty new to mathematics, so I'm probably missing something really obvious, but it's better to make the mistakes now than in my exam!