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- Thread starter Rujaxso
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When you square a binomial, the following rule applies:Not sure where the 2ah is coming from in the middle step.

f(a+h)=-5(a+h)^2+2(a+h)-1=-5(a^2 + 2ah +h^2) +2a +2h -1=-5a^2 - 10ah -5h^2 +2a +2h -1

Please enlighten me

\(\displaystyle (x+y)^2=x^2+2xy+y^2\)

Have you seen this rule before?

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- Jan 30, 2018

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BtwWhen you square a binomial, the following rule applies:

\(\displaystyle (x+y)^2=x^2+2xy+y^2\)

Have you seen this rule before?

Found this under Algebra 1 > polynomials > special products on khan academy, ...I will go over that section

- Jan 30, 2018

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Yes, that's what theOkay so instead of squaring each term I need to think about the quantity as a whole in the parenthesis as being a base for the exponent?

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Thinking that:I guess I wanted to apply A(B+C) = AB + AC to (B+C)^2 and make B^2 + C^2 which is incorrect I see.

\(\displaystyle (x+y)^n=x^n+b^n\)

is a mistake so commonly made by students, it's been given a name...the "freshman's dream."

I have also seen a lot of students make a related mistake, and that is to state:

\(\displaystyle \sqrt{x^2+y^2}=x+y\)

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