Posted by **Sandrine** on Wednesday, September 16, 2009 at 7:44pm.

How come when you find the square of the binomial (2x-5y)^2, the answer is 4x^2-20xy+25y^2 (according to my book)? I would think that the middle term, 2(2x-5y) would be 4x-10y, but my book says it is -20xy. But I thought you 2x and 5y were separate terms so you can't combine them like that by multiplying them together to form -20xy. Please explain why this is. Thanks!

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