
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
Observe the following equations:  
1=1  
1-4=-（1+2）=-3  
1-4+9=1+2+3=6  
1-4+9-16=-（1+2+3+4）=-10  
Then, the 5th equation is      
The value of the 20th equation is      
These equations reflect a certain pattern among integers. Let $n$ represent a positive integer, try to express the pattern you discovered using an equation related to $n$.

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