
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 that the terminal side of angle $α$ passes through point $P\left( \frac{4}{5}, -\frac {3}{5}\right)$,  
$(1)$ Find the value of $\sin α$;  
$(2)$ Find the value of $\frac{\sin\left(\frac{π}{2} - α\right)}{\sin\left(α + π\right)} - \frac{\tan\left(α - π\right)}{\cos\left(3π - α\right)}$.

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