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Accentuating the positive

Q Perhaps you can give a good explanation of why - 1 x - 1 = +1. I once asked a University senior lecturer in pure mathematics - his answer was "because it does"! I have my own way of explaining it perhaps - I can enhance that with yours.

A We can think of multiplying using integers that is (the negative numbers, zero, positive numbers) in a number of different ways. I have presented two examples shown right, although I believe the first doesn't provide me with a satisfactory reason why a negative number multiplied by a negative number equals a positive number.

Wendy Fortescue-Hubbard is a teacher, game inventor and member of the London Mathematical Society. She has been awarded a three-year fellowship by the National endowment for Science, Technology and the Arts (NESTA) to spread maths to the masses. Email your questions to Mathagony Aunt at Or write to TES Teacher, Admiral House, 66-68 East Smithfield, London E1W 1BX

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