SOLUTION: When finding the volume of a box; (20-2x)(16-2x)(x) 1st term(20times16) = 320 3ed term(-2xtimes-2x)=+4x^2

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Question 262879: When finding the volume of a box; (20-2x)(16-2x)(x) 1st term(20times16) = 320
3ed term(-2xtimes-2x)=+4x^2

How come the 2ed term is -72x??? I don't see the math. thank you
Answer by palanisamy(496) About Me  (Show Source):
You can put this solution on YOUR website!
(20-2x)(16-2x)(x)= (320-40x-32x+4x^2)*x
= (320-72x+4x^2)*x
= 320x-72x^2+4x^3