To simplify the expression \( (9x^2 - 6x + 2) - (x^2 + 4x - 39) \), we first distribute the negative sign across the second polynomial:
\[ = 9x^2 - 6x + 2 - x^2 - 4x + 39 \]
Now, we can combine like terms:
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Combine the \(x^2\) terms: \[ 9x^2 - x^2 = 8x^2 \]
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Combine the \(x\) terms: \[ -6x - 4x = -10x \]
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Combine the constant terms: \[ 2 + 39 = 41 \]
Putting it all together, we get:
\[ 8x^2 - 10x + 41 \]
Thus, the difference of the polynomials is:
\[ \boxed{8x^2 - 10x + 41} \]