Methods Notation

[BlakePre]

For practice exams, when I want to sub in a value into the derivative of let’s say y, then I’ll write dy/dx|x=a = ~~~

Does anyone know if this notation is allowed, or would I lose marks?

[Sine]

For practice exams, when I want to sub in a value into the derivative of let’s say y, then I’ll write dy/dx|x=a = ~~~

Does anyone know if this notation is allowed, or would I lose marks?

This is fine imo - and I have used it during exams (not 100% certain whether I needed to use it in the actual exam though).
If you are worried about it you can say let dy/dx = f'(x) and use f'(a)