To multiply the polynomial expression \((x + 2)(x - 4)\), we can use the distributive property (also known as the FOIL method for binomials).
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First: Multiply the first terms: \[ x \cdot x = x^2 \]
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Outer: Multiply the outer terms: \[ x \cdot (-4) = -4x \]
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Inner: Multiply the inner terms: \[ 2 \cdot x = 2x \]
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Last: Multiply the last terms: \[ 2 \cdot (-4) = -8 \]
Now, combine all these results: \[ x^2 + (-4x) + 2x - 8 \]
Combine like terms \((-4x + 2x)\): \[ x^2 - 2x - 8 \]
Thus, the product of \((x + 2)(x - 4)\) is: \[ \boxed{x^2 - 2x - 8} \]