
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 the polar coordinate system, it is known that point $A(2, \frac{\pi}{2})$, and point $B$ is on the line $l$: $\rho\cos\theta+\rho\sin\theta=0 (0\leqslant\theta\leqslant2\pi)$. When the length of segment $AB$ is the shortest, find the polar coordinates of point $B$.

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