Now if you try to find the product of either 10- x by 10 or 10+x by 10, the first product is 100-10x and the other 100+10x. Further some one may ask, how much is the product of 10-x by 10+x? You proceed thus: 10 by 10, 100 units, and negative x by 10 gives negative 10x; also 10 by x gives 10x positive, and negative x by x gives negative x^2. This total then equals 100 units less x^2
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