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Thread: HW help plz
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Old 12-13-2007   #3
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Default Watch your formulas

You wrote (a-b)^2 = a^2 + 2ab - b^2 but that is wrong. Was it like that all the time and I did not notice before?
(a-b)^2 = a^2 - 2ab + b^2

On the other hand, I agree that (a + b)^2 = a^2 + 2ab + b^2
I see that as the square of a sum being equal to the sum of two squares plus two rectangles. If I have a square garden with sides measuring a (area = a^2), and I want to make it bigger, I can add two rectangles of length a and width b to the South and East sides (area = ab for each one) and a square of side b (area = b^2) to fill the Southeast corner. I end up with a square garden of side a+b. The area is (a+b)^2, and equals the sums of the areas of the two squares and two rectangles listed above.