Chapter 5 - Section 5.4 - Multiplying Polynomials - Exercise Set - Page 290: 116

$5x^4+25x^3-10x^2-50x$

Using the given functions, then, \begin{align*} P(x)\cdot R(x)\cdot Q(x)=5x(x+5)(x^2-2) \\= (5x^2+25x)(x^2-2) \\= (5x^2)(x^2)+(5x^2)(-2)+(25x)(x^2)+(25x)(-2) \\= 5x^4-10x^2+25x^3-50x \\= 5x^4+25x^3-10x^2-50x .\end{align*}