To find \((f - g)(x)\), we need to subtract the function \(g(x)\) from the function \(f(x)\).
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Define the functions:
- \( f(x) = x^2 - 4x - 21 \)
- \( g(x) = x - 7 \)
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Subtract the functions: \[ (f - g)(x) = f(x) - g(x) \] \[ = (x^2 - 4x - 21) - (x - 7) \]
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Distribute the negative sign: \[ = x^2 - 4x - 21 - x + 7 \]
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Combine like terms:
- Combine \( -4x \) and \( -x \)
- Combine \( -21 \) and \( +7 \) \[ = x^2 - 5x - 14 \]
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Final result: Thus, \((f - g)(x) = x^2 - 5x - 14\).
The polynomial in simplest form is: \[ \boxed{x^2 - 5x - 14} \]