
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
Reading Comprehension:  
Calculate the value of $(x+y)(x-2y)-my(nx-y)$ (where $m, n$ are constants). When substituting the values of $x, y$ for calculation, both Xiao Ming and Xiao Liang mistakenly read the value of $y$, but the result was still 25. Careful Xiao Min substituted the correct values of $x, y$ for calculation, and the result was exactly 25. Out of curiosity, she then randomly changed the value of $y$ to 2006, and strangely enough, the result was still 25.  
(1) Based on the above situation, try to explore the mystery within;  
(2) Can you determine the values of $m, n$, and $x$?

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