
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
The function $f(x)=({m}^{2}-m-1){x}^{{m}^{2}+m-3}$ is a power function. For any $x_{1}$, $x_{2}\in \left(0,+\infty \right)$, and $x_{1}\neq x_{2}$, it satisfies $\frac{f({x}_{1})-f({x}_{2})}{{x}_{1}-{x}_{2}}＜0$. If $a$, $b\in R$, and $a \lt 0 \lt b$, $|a| \lt |b|$, determine the value of $f\left(a\right)+f\left(b\right)$.

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