1. The problem statement, all variables and given/known data 2. Relevant equations none 3. The attempt at a solution I literally just posted this in the thread: https://www.physicsforums.com/threads/proving-identities.881951/ But since it was marked solved I doubt anyone will see it. So sorry in advance for making a new thread on the same question. Ok, I am proving the exact same identity as the thread mentioned above, I looked through it and the explanations were very helpful. I have written out the answer, and would just like to know if I have written it properly as the answers in the thread were a bit jumbled, so I just want to make sure I am following correctly. Thanks.