Do the Edexcel maths papers have set topics (like in biology, cell biology and infection and response are always in Paper 1) does this happen in maths? If so which topics come under which paper.
No. In GCSE, any topic can come up in any paper, although with slight exceptions- you won't get a question about rationalising a denominator in a calculator paper.
No. In GCSE, any topic can come up in any paper, although with slight exceptions- you won't get a question about rationalising a denominator in a calculator paper.