Why couldn't it be a 1?

Calculus Level 4

\[ \large \displaystyle \int_{0}^{1} x^5 (2-x)^4 \, dx \]

If the above integral can be expressed in the form \( \dfrac{a}{b} \), where \(a\) and \(b\) are coprime positive integers, find \(a+b\).