To find the product of the expressions \((-g^3)\) and \((-2g^4)\), you can follow these steps:
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Multiply the coefficients: \(-1\) and \(-2\) give \(2\) (since the product of two negative numbers is positive).
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Multiply the variables: \(g^3 \cdot g^4 = g^{3+4} = g^7\) (using the property of exponents that states \(a^m \cdot a^n = a^{m+n}\)).
Now combine these results:
\[ (-g^3)(-2g^4) = 2g^7 \]
Thus, the simplified product is:
\[ \boxed{2g^7} \]