FYI...
I was taught a different way of remembering the sin, cos & tan formulae.
O/H = Sin (Orange Have Segments)
A/H = Cos (Apples Have Cores)
O/A = Tan (Oranges are Tasty)
I hope it helps.
BTW, it's not the maths that makes the ATPL's tricky, it's the volume of knowledge you need stuffed into your head.
Having said that it will definitely help if you can transpose formulae without thinking too much about it.