Answer
$a^5$
Work Step by Step
$a^5=\underline a\times\underline a\times\underline a\times\underline a\times\underline a$
$a^5=\underline a\times\underline a\times\underline a\times\underline a\times\underline a$
$a^5=\underline a\times\underline a\times\underline a\times\underline a\times\underline a$
$GCF=\underline a\times\underline a\times\underline a\times\underline a\times\underline a=a^5$