Posted by Sandrine on .
How come when you find the square of the binomial (2x5y)^2, the answer is 4x^220xy+25y^2 (according to my book)? I would think that the middle term, 2(2x5y) would be 4x10y, 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!

Algebra 
bobpursley,
FOIL: (x+y)^2= x^2+2xy+y^2