Chapter 1 - Introduction to Algebraic Expressions - 1.8 Exponential Notation and Order of Operations - 1.8 Exercise Set - Page 67: 82

$0$

Substituting $ a $ with $ -2 $ in the given expression, $ \dfrac{a^3-4a}{a(a-3)} $, then, \begin{array}{l}\require{cancel} \dfrac{(-2)^3-4(-2)}{-2(-2-3)} \\\\= \dfrac{-8+8}{-2(-5)} \\\\= \dfrac{0}{-2(-5)} \\\\= 0 .\end{array}