
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 opposite sides of angles $A$, $B$, and $C$ are $a$, $b$, and $c$ respectively, satisfying $\cos B + \sin(\frac{A+C}{2}) = 0$.  
$(1)$ Find the value of angle $B$.  
$(2)$ If the ratio of the altitudes on sides $AB$ and $BC$ is $3:5$, and $b=7$, find the area of $\triangle ABC$.

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