To simplify the expression \( 6i \cdot (-4)i \), we can start by treating the imaginary unit \( i \) properly.
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First, combine the coefficients: \[ 6 \cdot (-4) = -24 \]
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Next, combine the powers of \( i \): \[ i \cdot i = i^2 \] And since \( i^2 = -1 \), we have: \[ -24 \cdot i^2 = -24 \cdot (-1) = 24 \]
Putting it all together, we find: \[ 6i \cdot (-4)i = 24 \]
Thus, the simplified result is: \[ \boxed{24} \]