
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 acute-angled triangle $ABC$, the lengths of the sides opposite to angles $A$, $B$, and $C$ are $a$, $b$, and $c$ respectively, and $\sin A = \frac{\sqrt{7}}{4}$, $\sin C = \frac{3\sqrt{7}}{8}$.

1. Find the value of $\sin B$.
2. If $| \overset{→}{AC}+ \overset{→}{BC}|=2 \sqrt{23}$, find the length of the midline of edge $BC$.

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