
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
Among the following four conclusions, the correct one is ____.<br/>①$4^{x}=a$,$8^{y}=b$, then $2^{2x-3y}$ can be expressed as $\frac{a}{b}$.<br/>②The result of $\left(x-1\right)(x^{2}+ax+1)$ does not contain the term $x^{2}$, then $a=1$;<br/>③If $a+b=4$ and $ab=\frac{{15}}{4}$, then $a-b=1$;<br/>④If $\left(5-a\right)^{2a-4}=1$, then $a$ is $2$ or $4$;

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