## Precalculus: Concepts Through Functions, A Unit Circle Approach to Trigonometry (3rd Edition)

$0.9$
As $\sin (\theta+2\pi)=\sin(\theta+4\pi)=\sin\theta$, then $\sin\theta+\sin(\theta+2\pi)+\sin(\theta+4\pi)=\sin{\theta}+\sin{\theta}+\sin{\theta}=3\sin\theta=3(0.3)=0.9$