Elementary and Intermediate Algebra: Concepts & Applications (6th Edition)

$8^{10}n^{10}$
Since $a^x\cdot a^y=a^{x+y}$, then the given expression, $(8n)(8n)^{9}$, simplifies to \begin{array}{l}\require{cancel} (8n)^{1+9} \\\\= (8n)^{10} .\end{array} Since $(ab)^x=a^xb^x$, then the expression above simplifies to \begin{array}{l}\require{cancel} 8^{10}n^{10} .\end{array}