
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 $a$, $b$, $c$ are the opposite sides of angles $A$, $B$, $C$ in triangle $ABC$, and $\frac{a-c}{b-\sqrt{2}c}=\frac{sin(A+C)}{sinA+sinC}$.  
$(Ⅰ)$ Find the measure of angle $A$;  
$(Ⅱ)$ If $a=\sqrt{2}$, $O$ is the circumcenter of triangle $ABC$, find the minimum value of $|3\overrightarrow{OA}+2\overrightarrow{OB}+\overrightarrow{OC}|$;  
$(Ⅲ)$ Under the condition of $(Ⅱ)$, $P$ is a moving point on the circumcircle of triangle $ABC$, find the maximum value of $\overrightarrow{PB}•\overrightarrow{PC}$.

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