Apply the formula: $\int\sin\left(\theta \right)^n\cos\left(\theta \right)^mdx$$=\frac{-\sin\left(\theta \right)^{\left(n-1\right)}\cos\left(\theta \right)^{\left(m+1\right)}}{n+m}+\frac{n-1}{n+m}\int\sin\left(\theta \right)^{\left(n-2\right)}\cos\left(\theta \right)^mdx$, where $m=3$ and $n=9$
The integral $\frac{2}{3}\int\sin\left(x\right)^{7}\cos\left(x\right)^3dx$ results in: $-\frac{1}{15}\sin\left(x\right)^{6}\cos\left(x\right)^{4}-\frac{1}{20}\sin\left(x\right)^{4}\cos\left(x\right)^{4}+\frac{-\sin\left(x\right)^{2}\cos\left(x\right)^{4}}{30}+\frac{-\cos\left(x\right)^{4}}{60}$