## College Algebra (10th Edition)

$\dfrac{-2x^2+10x+18}{x^4+18x^2+81}$
$\bf{\text{Solution Outline:}}$ To simplify the given expression, $\dfrac{(x^2+9)\cdot2-(2x-5)\cdot2x}{(x^2+9)^2} ,$ use the Distributive Property first. Then remove the grouping symbols and combine like terms. Finally, use special products to simplify the denominator. $\bf{\text{Solution Details:}}$ Using the Distributive Property which is given by $a(b+c)=ab+ac,$ the expression above is equivalent to \begin{array}{l}\require{cancel} \dfrac{(x^2\cdot2+9\cdot2)-(2x\cdot2x-5\cdot2x)}{(x^2+9)^2} \\\\= \dfrac{(2x^2+18)-(4x^2-10x)}{(x^2+9)^2} .\end{array} Removing the grouping symbols and then combining like terms, the expression above is equivalent to \begin{array}{l}\require{cancel} \dfrac{2x^2+18-4x^2+10x}{(x^2+9)^2} \\\\= \dfrac{-2x^2+10x+18}{(x^2+9)^2} .\end{array} Using the square of a binomial which is given by $(a+b)^2=a^2+2ab+b^2$ or by $(a-b)^2=a^2-2ab+b^2,$ the expression above is equivalent to \begin{array}{l}\require{cancel} \dfrac{-2x^2+10x+18}{(x^2)^2+2(x^2)(9)+(9)^2} \\\\= \dfrac{-2x^2+10x+18}{x^4+18x^2+81} .\end{array}