
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
Point M (0,2) is on circle C: (x-4)^2+(y+1)^2 = 25. The tangent line l passes through M, and l is parallel to line l': 4x-ay+2=0. Find the distance between lines l and l'.

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