Zoe...
That would be zero... because in your sequence you would have (x-x) and that would be zero so anything times it would also be zero...
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Ok... take 18 toothpicks and arrange them in the following pattern... (6 toothpicks per 'box' with one 'crossing' the other one in the middle)... Now take away NINE toothpicks and have TEN left... ;^Ð
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