Chapter 5 - Section 5.5 - The Greatest Common Factor and Factoring by Grouping - Exercise Set - Page 294: 1

$a^{3}$

$a^{8}=(a\times a \times a) \times a \times a \times a \times a \times a $ $a^{5}=(a\times a \times a) \times a \times a$ $a^{3}=(a\times a \times a)$ When all monomials are in terms of $a$ and there are no other variables involved, the GCF is the monomial with the lowest exponent because the other monomials can be divided by it.