
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 \( a \), \( b \), and \( c \), respectively. The following conditions are given:
\[ (2a - c) \cos B = b \cos C \]
\[ \sin^2 A = \sin^2 B + \sin^2 C - \lambda \sin B \sin C \quad (\lambda \in \mathbf{R}) \]

1. Find the measure of angle \( B \).
2. If \( \lambda = \sqrt{3} \), determine the shape of triangle \( \triangle ABC \).
3. If triangle \( \triangle ABC \) is an obtuse triangle, determine the range of values for the real number \( \lambda \).

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