
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 a triangle $ABC$, if there exists a triangle $A_1B_1C_1$ such that $\dfrac{\cos A}{\sin A_1}= \dfrac{\cos B}{\sin B_1}= \dfrac{\cos C}{\sin C_1}=1$, then triangle $A_1B_1C_1$ is called a "dual" triangle of triangle $ABC$. If an isosceles triangle $ABC$ has a "dual" triangle, then the radian measure of its base angle is ______.

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