I've encountered a question about electrostatic forces on vertices of an equilateral triangle and I believe that I solved it correctly but my Physics teacher has marked it as incorrect. Am I correct? Amy clue why my Physics teacher marked it wrong? This is the question and the Physics teacher's marking of my answer. I attached the entire thing.
F = KQ1Q2/r^2
The Attempt at a Solution
The attempt of the solution is attached down with the teacher's marking.