Heh. I was kinda combining half my trapezium half-solution and half my interior-angles half-solution that I had already written - I think in the process I pruned out too much information. Including "F", and some of the steps that really would have explained the process a bit better.
Anyway - is there a nicer way of working this out? All that's a bit convoluted...
Given that:
re(2): To Charadenine
