
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 $0 < \alpha < \frac{\pi}{2}$, $\sin \alpha= \frac{4}{5}$.  
(I) Find the value of $\tan \alpha$;  
(II) Find the value of $\frac{\sin (\alpha+\pi)-2\cos ( \frac{\pi}{2}+\alpha)}{-\sin (-\alpha )+\cos (\pi +\alpha )}$.

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