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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 teacher@tes.co.uk Or write to TES Teacher, Admiral House, 66-68 East Smithfield, London E1W 1BX

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