Answer
$a-a^{2}$
Work Step by Step
We can use the product rule to simplify, which holds that $a^{m}\times a^{n}=a^{m+n}$ (where a is a real number, and m and n are positive integers).
$a^{\frac{1}{4}}(a^{\frac{3}{4}}-a^{\frac{7}{4}})=(a^{\frac{1}{4}}\times a^{\frac{3}{4}})-(a^{\frac{1}{4}}\times a^{\frac{7}{4}})=(a^{\frac{1}{4}+\frac{3}{4}})-(a^{\frac{1}{4}+\frac{7}{4}})=a^{\frac{4}{4}}-a^{\frac{8}{4}}=a-a^{2}$
