Chapter 4 - Section 4.1 - Integer Exponents and Scientific Notation - 4.1 Exercises - Page 278: 122

$-\dfrac{15}{a^4}$

Using the laws of exponents, the given expression, $ 3a^2(-5a^{-6})(-2a)^0 ,$ is equivalent to \begin{array}{l}\require{cancel} 3a^2(-5a^{-6})(1) \\\\= -15a^{2+(-6)} \\\\= -15a^{2-6} \\\\= -15a^{-4} \\\\= -\dfrac{15}{a^4} .\end{array}