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#1 2014-12-28 02:47:24

albmsr
Guest

distributive property vs multiplication of polynomials

Hello, I was solving an equation from MathsIsFun and I got to this step: x(1-7x) = 5-7x(x+2). This is where I drifted from the correct resolution.
I attempted to do a distributive on the right side, like this: 5-7x(x+2) -> -7x*x + 7x*2. According to the official resolution, 5-7x(x+2) should be "processed" as (5-7x)(x+2), and not as 7x(x+2) as I did. In other words, I interpreted the expression 5-7x(x+2) as in need of the distributive of 7x(x+2), whereas the official resolution interpreted the expression 5-7x(x+2) as a multiplication of polynomials (5-7x)(x+2).

My doubt is: When I face an expression like 5-7x(x+2), how do I know whether I should "see" a multiplication of polynomials there or starting doing a distributive of the term exactly on the left side of the parenthesis?

Thanks!

#2 2014-12-28 02:53:34

bobbym
bumpkin
From: Bumpkinland
Registered: 2009-04-12
Posts: 109,606

Re: distributive property vs multiplication of polynomials

Hi;

5-7x(x+2) -> -7x*x + 7x*2

What happened to the 5 on the left hand side?


In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

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#3 2014-12-28 05:26:06

albmsr
Member
Registered: 2014-12-28
Posts: 1

Re: distributive property vs multiplication of polynomials

In this case I left the 5 there to plug the result of the distributive. So I would work it out like this: 5-7x(x+2) -> doing the distributive of 7x(x+2) results in -7x*x + 7x*2 -> so 5-7x(x+2) would become 5 - 7x*x + 7x*2

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#4 2014-12-28 06:38:04

bobbym
bumpkin
From: Bumpkinland
Registered: 2009-04-12
Posts: 109,606

Re: distributive property vs multiplication of polynomials

Hi;

That is not correct.

Also, that factorization you gave is not correct.

Please copy the problem exactly how it appears or provide a link for further help.


In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

Offline

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