
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
In triangle \( \triangle ABC \), with sides \( a \), \( b \), \( c \) opposite angles \( A \), \( B \), \( C \) respectively, it is given that 
\[ 2\cos^2 \frac{A-B}{2}\cos B - \sin(A-B)\sin B + \cos(A+C) = -\frac{3}{5}.\]
If \( a = 8 \) and \( b = \sqrt{3} \), then \( \angle B \) is \_\_\_\_\_\_.

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