For Edexcel A-level Maths, will they ever ask you to work out the suitable substitution or will it always be given to you?
They could do I think. If they don't tell you then it should be a somwhat obvious one e.g subbing for whatever's in the brackets. I would just practise it, leave nothing to chance
i’ve looked at all previous edexcel questions and i’ve never seen a question without the substitution provided, but i’d follow the other advice and just practice figuring out the correct one in case it’s not given to you