To simplify the polynomial \((3x^2 - 2x - 5) + (2x^2 + x - 10)\), we will combine like terms.
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Combine the \(x^2\) terms: \[ 3x^2 + 2x^2 = 5x^2 \]
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Combine the \(x\) terms: \[ -2x + x = -x \]
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Combine the constant terms: \[ -5 - 10 = -15 \]
Putting it all together, we have: \[ 5x^2 - x - 15 \]
So the simplified polynomial in standard form is: \[ \boxed{5x^2 - x - 15} \]