
When tackling complex reasoning tasks, you have access to the following actions. Use them as needed to progress through your thought process.

[ASSESS]

[ADVANCE]

[VERIFY]

[SIMPLIFY]

[SYNTHESIZE]

[PIVOT]

[OUTPUT]

You should strictly follow the format below:

[ACTION NAME]

# Your action step 1

# Your action step 2

# Your action step 3

...

Next action: [NEXT ACTION NAME]


system
Given that in $\triangle ABC$, the internal angle $B$ satisfies $2\cos 2B-8\cos B+5=0$. If $\overrightarrow{BC}=\overrightarrow{a}$, $\overrightarrow{CA}=\overrightarrow{b}$, and $\overrightarrow{a}$, $\overrightarrow{b}$ satisfy $\overrightarrow{a} \cdot \overrightarrow{b}=-9$, $|\overrightarrow{a}|=3$, $|\overrightarrow{b}|=5$, and $\theta$ is the angle between $\overrightarrow{a}$ and $\overrightarrow{b}$,

1. Find the measure of angle $B$,
2. Find $\sin(B+\theta)$.

Present the answer in LaTex format: \boxed{Your answer}
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