
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 $\triangle ABC$, the sides opposite angles $A$, $B$, and $C$ are denoted as $a$, $b$, and $c$ respectively. It is given that $a=5$, $b=6$, and $\cos B=-\frac{4}{5}$.  
$(Ⅰ)$ Find the value of angle $A$.  
$(Ⅱ)$ Find the value of $c$.  
$(Ⅲ)$ Find the value of $\sin \left(2B+A\right)$.

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