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Mathematics 17 Online
OpenStudy (anonymous):

Simplify the rational expression. State any restrictions on the variable.

OpenStudy (anonymous):

\[\frac{ n^4-10n^2+24 }{ n^4-9^2+18 }\]

OpenStudy (math&ing001):

First lets find the restrictions. For that we solve for n : n^4 - 9^2 + 18 = 0

OpenStudy (anonymous):

Than what? @math&ing001

OpenStudy (anonymous):

OpenStudy (anonymous):

OpenStudy (anonymous):

OpenStudy (anonymous):

OpenStudy (anonymous):

@Hero

OpenStudy (anonymous):

@satellite73

hero (hero):

Let \(n^2 = y\) then try simplifying the expression.

OpenStudy (anonymous):

Please help me I know its \[\frac{ n^2-4 }{ n^2-3}\] but i dont know the other half for my answer, so it's between A-C for the answer

OpenStudy (anonymous):

(n+2)(n−2)(n2−6) (n2−3)(n2−6)

hero (hero):

How do you know it's \(\dfrac{n^2 - 4}{n^2 - 3}\)?

OpenStudy (anonymous):

(n+2)(n−2)(n2−6) (n2−3)(n2−6)

hero (hero):

Multiply it back out to see if what you get matches the original expression.

hero (hero):

Also the original expression you posted likely has a typo in it somewhere.

OpenStudy (anonymous):

How do i do that?

OpenStudy (anonymous):

@timo86m

OpenStudy (anonymous):

@Astrophysics

OpenStudy (anonymous):

@Michele_Laino can you please help me finish my math problem?

OpenStudy (anonymous):

@mathmate

OpenStudy (anonymous):

I just need help with the end of the problem. I think the answer is B though

OpenStudy (mathmate):

@EllenJaz17 Please confirm that the problem is indeed: \(\Large \frac{ n^4-10n^2+24 }{ n^4-9\color{red}{n}^2+18 } \)

OpenStudy (anonymous):

yes

OpenStudy (anonymous):

Yes it is @mathmate

OpenStudy (michele_laino):

hint: we can factorize the denominator, using the same procedure for numerator, so we can write this: \[{n^4} - 9{n^2} + 18 = \left( {{n^2} - 6} \right)\left( {{n^2} - 3} \right)\]

OpenStudy (anonymous):

(n+2)(n−2)(n2−6) (n2−3)(n2−6)

OpenStudy (anonymous):

\[\frac{ n^2-4 }{ n^2-3 }\]

OpenStudy (michele_laino):

yes!

OpenStudy (anonymous):

I know thats the answer to the first half but i need to find out the second half

OpenStudy (anonymous):

OpenStudy (anonymous):

OpenStudy (anonymous):

OpenStudy (anonymous):

OpenStudy (michele_laino):

the denominator is equal to zero when these two conditions hold: \[\begin{gathered} {n^2} - 6 = 0 \hfill \\ \hfill \\ {n^2} - 3 = 0 \hfill \\ \end{gathered} \]

OpenStudy (michele_laino):

please remember, that we can not divide by zero

OpenStudy (anonymous):

correct

OpenStudy (michele_laino):

please solve those quadratic equations for n, what do you get?

OpenStudy (anonymous):

6 and 3?

OpenStudy (michele_laino):

are you sure? we have 6^2= 36, and 3^2=9

OpenStudy (anonymous):

No im not sure im just guessing

OpenStudy (michele_laino):

hint: the solution to this equation: \[{n^2} - k = 0\] are: \[n = \sqrt k ,\quad n = - \sqrt k \]

OpenStudy (michele_laino):

solutions*

OpenStudy (michele_laino):

since: \[{\left( {\sqrt k } \right)^2} = {\left( { - \sqrt k } \right)^2} = {n^2}\]

OpenStudy (michele_laino):

being k a positive number or k=0

OpenStudy (anonymous):

So is it answer B?

OpenStudy (michele_laino):

no, I don't think so, sorry!

OpenStudy (anonymous):

OpenStudy (michele_laino):

hint: what are the solution of this equation: \[{n^2} - 3 = 0\] ?

OpenStudy (anonymous):

So that only leaves A & C correct? because D isn't \[\frac{ n^2-4 }{ n^2-3 }\]

OpenStudy (michele_laino):

solutions*

OpenStudy (anonymous):

\[n^{2}=3?\]

OpenStudy (michele_laino):

yes! and what is n=...?

OpenStudy (anonymous):

\[n \neq \pm \sqrt{6}\pm \sqrt{3}?\]

OpenStudy (michele_laino):

from this equation: \[{n^2} - 3 = 0\] I get \[n = \pm \sqrt 3 \] am I right?

OpenStudy (anonymous):

yes

OpenStudy (michele_laino):

ok! so we have to exclude those 2 values, since when: \[n = \pm \sqrt 3 \] the denominator is zero Now do the same with the equation: \[{n^2} - 6 = 0\]

OpenStudy (anonymous):

\[n=\pm \sqrt{6}\]

OpenStudy (michele_laino):

perfect, we have to exclude those values too, since when: \[n = \pm \sqrt 6 \] the denominator is zero. So what is the right option?

OpenStudy (anonymous):

A

OpenStudy (michele_laino):

that's right! :)

OpenStudy (anonymous):

Thank you so much for teaching me how to get to the answer!

OpenStudy (michele_laino):

:)

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