To find the product of the expressions \((2q^9 + 3q^7)(-6q^2 + 9)\), we can use the distributive property (also known as the FOIL method for binomials). We will multiply each term in the first expression by each term in the second expression.
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Multiply \(2q^9\) by each term in \(-6q^2 + 9\):
- \(2q^9 \cdot (-6q^2) = -12q^{11}\)
- \(2q^9 \cdot 9 = 18q^9\)
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Multiply \(3q^7\) by each term in \(-6q^2 + 9\):
- \(3q^7 \cdot (-6q^2) = -18q^{9}\)
- \(3q^7 \cdot 9 = 27q^7\)
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Add all the products together: \[ -12q^{11} + 18q^9 - 18q^9 + 27q^7 \]
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Combine like terms:
- Notice that \(18q^9\) and \(-18q^9\) cancel each other out.
- So the expression simplifies to: \[ -12q^{11} + 27q^7 \]
Thus, the final answer is: \[ \boxed{-12q^{11} + 27q^7} \]