Saturday, 25 January 2014

algebra precalculus - Best way to simplify a polynomial fraction divided by a polynomial fraction as completely as possible



I've been trying for the past few days to complete this question from a review booklet before I start university:




Simplify as completely as possible:





( 5x^2 -9x -2 / 30x^3 + 6x^2 ) / ( x^4 -3x^2 -4 / 2x^8 +6x^7 + 4x^6 )


However, I've only gotten as far as this answer below:



( (x -1) / 6x^2 ) / ((x^2 +1)(x^2 -4) / (2x^4 +4x^3)(x^4 + x^3))



I can't figure out how to simplify it further. What is the best / a good way to approach such a question that consists of a polynomial fraction divided by a polynomial fraction?



Is it generally a good idea to factor each fraction first then multiply them like I attempted above, or is it better to multiply them without factoring then try to simplify one big fraction?



Answer



\begin{align}
&\;\frac{ 5x^2 -9x -2 }{ 30x^3 + 6x^2 } \div \frac{ x^4 -3x^2 -4}{ 2x^8 +6x^7 + 4x^6 }\\
=&\;\frac{(x-2)(5x+1) }{ 6x^2(5x+1) } \times \frac{ 2x^6(x+1)(x+2)}{(x-2)(x+2)(x^2+1)}\\
=&\; \frac{x^4(x+1)}{3(x^2+1)}
\end{align}


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