# Chapter R - Section R.7 - Rational Expressions - R.7 Assess Your Understanding - Page 72: 92

$\dfrac{4x^3-15x^2}{4x^2-20x+25}$

#### Work Step by Step

$\bf{\text{Solution Outline:}}$ To simplify the given expression, $\dfrac{(2x-5)\cdot3x^2-x^3\cdot2}{(2x-5)^2} ,$ 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{(2x\cdot3x^2-5\cdot3x^2)-x^3\cdot2}{(2x-5)^2} \\\\= \dfrac{(6x^3-15x^2)-2x^3}{(2x-5)^2} .\end{array} Removing the grouping symbols and then combining like terms, the expression above is equivalent to \begin{array}{l}\require{cancel} \dfrac{6x^3-15x^2-2x^3}{(2x-5)^2} \\\\= \dfrac{4x^3-15x^2}{(2x-5)^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{4x^3-15x^2}{(2x)^2-2(2x)(5)+(5)^2} \\\\= \dfrac{4x^3-15x^2}{4x^2-20x+25} .\end{array}

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