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Missing or incomplete working in 'show that' questions
“Candidates need to appreciate that every step of working needs to be clearly demonstrated in order to gain full marks for "show that" questions and that their final result needs to be what the question asked them to show in the first place.”— 9MA0 Paper 1, June 2023
How to fix: In 'show that' questions: (1) work TOWARDS the given answer, never from it; (2) show every algebraic manipulation as a separate line; (3) write the final statement that matches what was asked. For 'show that' questions worth 2 marks, one intermediate line is the minimum — stating 2.3r = 27.6 for a 2-mark arc question is not sufficient.