
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 $\theta$ passes through point $P(3a,4a)$ where $\left(a \gt 0\right)$.  
$(Ⅰ)$ Find the value of $\sin \theta$;  
$(Ⅱ)$ Find the value of $\sin\left({\frac{{3π}}{2}-θ}\right)+\cos\left({θ-π}\right)$.

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